feat(backend): Implement Sprint Aggregate Root and Domain Events (Task 1)

Created Sprint domain model with full business logic and validation:
- SprintId value object
- SprintStatus enum (Planned/Active/Completed)
- Sprint aggregate root with lifecycle management
- 7 domain events (Created, Updated, Started, Completed, Deleted, TaskAdded, TaskRemoved)

Business Rules Implemented:
- Sprint duration validation (1-30 days)
- Status transitions (Planned → Active → Completed)
- Task management (add/remove with validation)
- Cannot modify completed sprints

Story 3 Task 1/6 completed.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Aggregates/ProjectAggregate/Sprint.cs

@@ -0,0 +1,165 @@
+using ColaFlow.Shared.Kernel.Common;
+using ColaFlow.Modules.ProjectManagement.Domain.Exceptions;
+using ColaFlow.Modules.ProjectManagement.Domain.ValueObjects;
+using ColaFlow.Modules.ProjectManagement.Domain.Enums;
+using ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Aggregates.ProjectAggregate;
+
+/// <summary>
+/// Sprint Entity (part of Project aggregate)
+/// </summary>
+public class Sprint : Entity
+{
+    public new SprintId Id { get; private set; }
+    public TenantId TenantId { get; private set; }
+    public ProjectId ProjectId { get; private set; }
+    public string Name { get; private set; }
+    public string? Goal { get; private set; }
+    public DateTime StartDate { get; private set; }
+    public DateTime EndDate { get; private set; }
+    public SprintStatus Status { get; private set; }
+
+    private readonly List<TaskId> _taskIds = new();
+    public IReadOnlyCollection<TaskId> TaskIds => _taskIds.AsReadOnly();
+
+    public DateTime CreatedAt { get; private set; }
+    public UserId CreatedBy { get; private set; }
+    public DateTime? UpdatedAt { get; private set; }
+
+    // EF Core constructor
+    private Sprint()
+    {
+        Id = null!;
+        TenantId = null!;
+        ProjectId = null!;
+        Name = null!;
+        Status = null!;
+        CreatedBy = null!;
+    }
+
+    /// <summary>
+    /// Create a new Sprint
+    /// </summary>
+    public static Sprint Create(
+        TenantId tenantId,
+        ProjectId projectId,
+        string name,
+        string? goal,
+        DateTime startDate,
+        DateTime endDate,
+        UserId createdBy)
+    {
+        ValidateName(name);
+        ValidateDates(startDate, endDate);
+
+        return new Sprint
+        {
+            Id = SprintId.Create(),
+            TenantId = tenantId,
+            ProjectId = projectId,
+            Name = name,
+            Goal = goal,
+            StartDate = startDate,
+            EndDate = endDate,
+            Status = SprintStatus.Planned,
+            CreatedAt = DateTime.UtcNow,
+            CreatedBy = createdBy
+        };
+    }
+
+    /// <summary>
+    /// Update sprint details
+    /// </summary>
+    public void UpdateDetails(string name, string? goal, DateTime startDate, DateTime endDate)
+    {
+        if (Status.Name == SprintStatus.Completed.Name)
+            throw new DomainException("Cannot update a completed sprint");
+
+        ValidateName(name);
+        ValidateDates(startDate, endDate);
+
+        Name = name;
+        Goal = goal;
+        StartDate = startDate;
+        EndDate = endDate;
+        UpdatedAt = DateTime.UtcNow;
+    }
+
+    /// <summary>
+    /// Start the sprint (Planned → Active)
+    /// </summary>
+    public void Start()
+    {
+        if (Status.Name != SprintStatus.Planned.Name)
+            throw new DomainException($"Cannot start sprint in {Status.Name} status. Sprint must be in Planned status.");
+
+        Status = SprintStatus.Active;
+        UpdatedAt = DateTime.UtcNow;
+    }
+
+    /// <summary>
+    /// Complete the sprint (Active → Completed)
+    /// </summary>
+    public void Complete()
+    {
+        if (Status.Name != SprintStatus.Active.Name)
+            throw new DomainException($"Cannot complete sprint in {Status.Name} status. Sprint must be in Active status.");
+
+        Status = SprintStatus.Completed;
+        UpdatedAt = DateTime.UtcNow;
+    }
+
+    /// <summary>
+    /// Add a task to the sprint
+    /// </summary>
+    public void AddTask(TaskId taskId)
+    {
+        if (Status.Name == SprintStatus.Completed.Name)
+            throw new DomainException("Cannot add tasks to a completed sprint");
+
+        if (_taskIds.Any(t => t.Value == taskId.Value))
+            throw new DomainException("Task is already in this sprint");
+
+        _taskIds.Add(taskId);
+        UpdatedAt = DateTime.UtcNow;
+    }
+
+    /// <summary>
+    /// Remove a task from the sprint
+    /// </summary>
+    public void RemoveTask(TaskId taskId)
+    {
+        if (Status.Name == SprintStatus.Completed.Name)
+            throw new DomainException("Cannot remove tasks from a completed sprint");
+
+        var task = _taskIds.FirstOrDefault(t => t.Value == taskId.Value);
+        if (task == null)
+            throw new DomainException("Task is not in this sprint");
+
+        _taskIds.Remove(task);
+        UpdatedAt = DateTime.UtcNow;
+    }
+
+    private static void ValidateName(string name)
+    {
+        if (string.IsNullOrWhiteSpace(name))
+            throw new DomainException("Sprint name cannot be empty");
+
+        if (name.Length > 200)
+            throw new DomainException("Sprint name cannot exceed 200 characters");
+    }
+
+    private static void ValidateDates(DateTime startDate, DateTime endDate)
+    {
+        if (endDate <= startDate)
+            throw new DomainException("Sprint end date must be after start date");
+
+        var duration = (endDate - startDate).Days;
+        if (duration > 30)
+            throw new DomainException("Sprint duration cannot exceed 30 days");
+
+        if (duration < 1)
+            throw new DomainException("Sprint duration must be at least 1 day");
+    }
+}

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Enums/SprintStatus.cs

@@ -0,0 +1,35 @@
+namespace ColaFlow.Modules.ProjectManagement.Domain.Enums;
+
+/// <summary>
+/// Sprint Status
+/// </summary>
+public class SprintStatus
+{
+    public string Name { get; init; }
+
+    public static readonly SprintStatus Planned = new() { Name = "Planned" };
+    public static readonly SprintStatus Active = new() { Name = "Active" };
+    public static readonly SprintStatus Completed = new() { Name = "Completed" };
+
+    private SprintStatus() { Name = string.Empty; }
+
+    public static SprintStatus FromString(string status)
+    {
+        return status?.ToLowerInvariant() switch
+        {
+            "planned" => Planned,
+            "active" => Active,
+            "completed" => Completed,
+            _ => throw new ArgumentException($"Invalid sprint status: {status}", nameof(status))
+        };
+    }
+
+    public static IEnumerable<SprintStatus> GetAll()
+    {
+        yield return Planned;
+        yield return Active;
+        yield return Completed;
+    }
+
+    public override string ToString() => Name;
+}

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/SprintCompletedEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Sprint is completed
+/// </summary>
+public sealed record SprintCompletedEvent(Guid SprintId, string SprintName, Guid ProjectId, int TaskCount) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/SprintCreatedEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Sprint is created
+/// </summary>
+public sealed record SprintCreatedEvent(Guid SprintId, string SprintName, Guid ProjectId) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/SprintDeletedEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Sprint is deleted
+/// </summary>
+public sealed record SprintDeletedEvent(Guid SprintId, string SprintName, Guid ProjectId) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/SprintStartedEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Sprint is started
+/// </summary>
+public sealed record SprintStartedEvent(Guid SprintId, string SprintName, Guid ProjectId) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/SprintUpdatedEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Sprint is updated
+/// </summary>
+public sealed record SprintUpdatedEvent(Guid SprintId, string SprintName, Guid ProjectId) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/TaskAddedToSprintEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Task is added to a Sprint
+/// </summary>
+public sealed record TaskAddedToSprintEvent(Guid SprintId, Guid TaskId, Guid ProjectId) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/Events/TaskRemovedFromSprintEvent.cs

@@ -0,0 +1,8 @@
+using MediatR;
+
+namespace ColaFlow.Modules.ProjectManagement.Domain.Events;
+
+/// <summary>
+/// Event raised when a Task is removed from a Sprint
+/// </summary>
+public sealed record TaskRemovedFromSprintEvent(Guid SprintId, Guid TaskId, Guid ProjectId) : INotification;

colaflow-api/src/Modules/ProjectManagement/ColaFlow.Modules.ProjectManagement.Domain/ValueObjects/SprintId.cs

@@ -0,0 +1,25 @@
+namespace ColaFlow.Modules.ProjectManagement.Domain.ValueObjects;
+
+/// <summary>
+/// Sprint ID Value Object
+/// </summary>
+public sealed record SprintId
+{
+    public Guid Value { get; init; }
+
+    private SprintId(Guid value)
+    {
+        if (value == Guid.Empty)
+            throw new ArgumentException("SprintId cannot be empty", nameof(value));
+
+        Value = value;
+    }
+
+    public static SprintId Create() => new(Guid.NewGuid());
+
+    public static SprintId From(Guid value) => new(value);
+
+    public override string ToString() => Value.ToString();
+
+    public static implicit operator Guid(SprintId sprintId) => sprintId.Value;
+}