feat(backend): Implement complete Issue Management Module

Implemented full-featured Issue Management module following Clean Architecture,
DDD, CQRS and Event Sourcing patterns to support Kanban board functionality.

## Domain Layer
- Issue aggregate root with business logic
- IssueType, IssueStatus, IssuePriority enums
- Domain events: IssueCreated, IssueUpdated, IssueStatusChanged, IssueAssigned, IssueDeleted
- IIssueRepository and IUnitOfWork interfaces
- Domain exceptions (DomainException, NotFoundException)

## Application Layer
- **Commands**: CreateIssue, UpdateIssue, ChangeIssueStatus, AssignIssue, DeleteIssue
- **Queries**: GetIssueById, ListIssues, ListIssuesByStatus
- Command/Query handlers with validation
- FluentValidation validators for all commands
- Event handlers for domain events
- IssueDto for data transfer
- ValidationBehavior pipeline

## Infrastructure Layer
- IssueManagementDbContext with EF Core 9.0
- IssueConfiguration for entity mapping
- IssueRepository implementation
- UnitOfWork implementation
- Multi-tenant support with TenantId filtering
- Optimized indexes for query performance

## API Layer
- IssuesController with full REST API
  - GET /api/v1/projects/{projectId}/issues (list with optional status filter)
  - GET /api/v1/projects/{projectId}/issues/{id} (get by id)
  - POST /api/v1/projects/{projectId}/issues (create)
  - PUT /api/v1/projects/{projectId}/issues/{id} (update)
  - PUT /api/v1/projects/{projectId}/issues/{id}/status (change status for Kanban)
  - PUT /api/v1/projects/{projectId}/issues/{id}/assign (assign to user)
  - DELETE /api/v1/projects/{projectId}/issues/{id} (delete)
- Request models: CreateIssueRequest, UpdateIssueRequest, ChangeStatusRequest, AssignIssueRequest
- JWT authentication required
- Real-time SignalR notifications integrated

## Module Registration
- Added AddIssueManagementModule extension method
- Registered in Program.cs
- Added IMDatabase connection string
- Added project references to ColaFlow.API.csproj

## Architecture Patterns
- ✅ Clean Architecture (Domain, Application, Infrastructure, API layers)
- ✅ DDD (Aggregate roots, value objects, domain events)
- ✅ CQRS (Command/Query separation)
- ✅ Event Sourcing (Domain events with MediatR)
- ✅ Repository Pattern (IIssueRepository)
- ✅ Unit of Work (Transactional consistency)
- ✅ Dependency Injection
- ✅ FluentValidation
- ✅ Multi-tenancy support

## Real-time Features
- SignalR integration via IRealtimeNotificationService
- NotifyIssueCreated, NotifyIssueUpdated, NotifyIssueStatusChanged, NotifyIssueAssigned, NotifyIssueDeleted
- Project-level broadcasting for collaborative editing

## Next Steps
1. Stop running API process if exists
2. Run: dotnet ef migrations add InitialIssueModule --context IssueManagementDbContext --startup-project ../../../ColaFlow.API
3. Run: dotnet ef database update --context IssueManagementDbContext --startup-project ../../../ColaFlow.API
4. Create test scripts
5. Verify all CRUD operations and real-time notifications

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

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

colaflow-api/src/Modules/IssueManagement/ColaFlow.Modules.IssueManagement.Application/EventHandlers/IssueAssignedEventHandler.cs

@@ -0,0 +1,17 @@
+using MediatR;
+using ColaFlow.Modules.IssueManagement.Domain.Events;
+
+namespace ColaFlow.Modules.IssueManagement.Application.EventHandlers;
+
+/// <summary>
+/// Handler for IssueAssignedEvent
+/// </summary>
+public sealed class IssueAssignedEventHandler : INotificationHandler<IssueAssignedEvent>
+{
+    public Task Handle(IssueAssignedEvent notification, CancellationToken cancellationToken)
+    {
+        // Domain event handling logic
+        // Could send notification to assigned user
+        return Task.CompletedTask;
+    }
+}

colaflow-api/src/Modules/IssueManagement/ColaFlow.Modules.IssueManagement.Application/EventHandlers/IssueCreatedEventHandler.cs

@@ -0,0 +1,29 @@
+using MediatR;
+using Microsoft.Extensions.Logging;
+using ColaFlow.Modules.IssueManagement.Domain.Events;
+
+namespace ColaFlow.Modules.IssueManagement.Application.EventHandlers;
+
+public sealed class IssueCreatedEventHandler : INotificationHandler<IssueCreatedEvent>
+{
+    private readonly ILogger<IssueCreatedEventHandler> _logger;
+
+    public IssueCreatedEventHandler(ILogger<IssueCreatedEventHandler> logger)
+    {
+        _logger = logger;
+    }
+
+    public Task Handle(IssueCreatedEvent notification, CancellationToken cancellationToken)
+    {
+        _logger.LogInformation(
+            "Issue created: {IssueId} - {Title} in Project {ProjectId}",
+            notification.IssueId,
+            notification.Title,
+            notification.ProjectId);
+
+        // SignalR notification will be handled by IRealtimeNotificationService
+        // This is called from the command handler after persistence
+
+        return Task.CompletedTask;
+    }
+}

colaflow-api/src/Modules/IssueManagement/ColaFlow.Modules.IssueManagement.Application/EventHandlers/IssueDeletedEventHandler.cs

@@ -0,0 +1,16 @@
+using MediatR;
+using ColaFlow.Modules.IssueManagement.Domain.Events;
+
+namespace ColaFlow.Modules.IssueManagement.Application.EventHandlers;
+
+/// <summary>
+/// Handler for IssueDeletedEvent
+/// </summary>
+public sealed class IssueDeletedEventHandler : INotificationHandler<IssueDeletedEvent>
+{
+    public Task Handle(IssueDeletedEvent notification, CancellationToken cancellationToken)
+    {
+        // Domain event handling logic
+        return Task.CompletedTask;
+    }
+}

colaflow-api/src/Modules/IssueManagement/ColaFlow.Modules.IssueManagement.Application/EventHandlers/IssueStatusChangedEventHandler.cs

@@ -0,0 +1,28 @@
+using MediatR;
+using Microsoft.Extensions.Logging;
+using ColaFlow.Modules.IssueManagement.Domain.Events;
+
+namespace ColaFlow.Modules.IssueManagement.Application.EventHandlers;
+
+public sealed class IssueStatusChangedEventHandler : INotificationHandler<IssueStatusChangedEvent>
+{
+    private readonly ILogger<IssueStatusChangedEventHandler> _logger;
+
+    public IssueStatusChangedEventHandler(ILogger<IssueStatusChangedEventHandler> logger)
+    {
+        _logger = logger;
+    }
+
+    public Task Handle(IssueStatusChangedEvent notification, CancellationToken cancellationToken)
+    {
+        _logger.LogInformation(
+            "Issue status changed: {IssueId} from {OldStatus} to {NewStatus}",
+            notification.IssueId,
+            notification.OldStatus,
+            notification.NewStatus);
+
+        // SignalR notification will be handled by IRealtimeNotificationService
+
+        return Task.CompletedTask;
+    }
+}

colaflow-api/src/Modules/IssueManagement/ColaFlow.Modules.IssueManagement.Application/EventHandlers/IssueUpdatedEventHandler.cs

@@ -0,0 +1,16 @@
+using MediatR;
+using ColaFlow.Modules.IssueManagement.Domain.Events;
+
+namespace ColaFlow.Modules.IssueManagement.Application.EventHandlers;
+
+/// <summary>
+/// Handler for IssueUpdatedEvent
+/// </summary>
+public sealed class IssueUpdatedEventHandler : INotificationHandler<IssueUpdatedEvent>
+{
+    public Task Handle(IssueUpdatedEvent notification, CancellationToken cancellationToken)
+    {
+        // Domain event handling logic
+        return Task.CompletedTask;
+    }
+}