feat(backend): Add SignalR real-time notifications for Sprint events - Sprint 2 Story 3 Task 5

Implemented comprehensive SignalR notifications for Sprint lifecycle events.

Features:
- Extended IRealtimeNotificationService with 5 Sprint notification methods
- Implemented Sprint notification service methods in RealtimeNotificationService
- Created SprintEventHandlers to handle all 5 Sprint domain events
- Updated UpdateSprintCommandHandler to publish SprintUpdatedEvent
- SignalR events broadcast to both project and tenant groups

Sprint Events Implemented:
1. SprintCreated - New sprint created
2. SprintUpdated - Sprint details modified
3. SprintStarted - Sprint transitioned to Active status
4. SprintCompleted - Sprint transitioned to Completed status
5. SprintDeleted - Sprint removed

Technical Details:
- Event handlers catch and log errors (fire-and-forget pattern)
- Notifications include SprintId, SprintName, ProjectId, and Timestamp
- Multi-tenant isolation via tenant groups
- Project-level targeting via project groups

Frontend Integration:
- Frontend can listen to 'SprintCreated', 'SprintUpdated', 'SprintStarted', 'SprintCompleted', 'SprintDeleted' events
- Real-time UI updates for sprint changes

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

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

colaflow-api/src/ColaFlow.API/Services/RealtimeNotificationService.cs

@@ -202,6 +202,118 @@ public class RealtimeNotificationService : IRealtimeNotificationService
         });
     }
 
+    // Sprint notifications
+    public async Task NotifySprintCreated(Guid tenantId, Guid projectId, Guid sprintId, string sprintName)
+    {
+        var projectGroupName = $"project-{projectId}";
+        var tenantGroupName = $"tenant-{tenantId}";
+
+        _logger.LogInformation("Notifying sprint {SprintId} created in project {ProjectId}", sprintId, projectId);
+
+        await _projectHubContext.Clients.Group(projectGroupName).SendAsync("SprintCreated", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+
+        await _projectHubContext.Clients.Group(tenantGroupName).SendAsync("SprintCreated", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+    }
+
+    public async Task NotifySprintUpdated(Guid tenantId, Guid projectId, Guid sprintId, string sprintName)
+    {
+        var projectGroupName = $"project-{projectId}";
+
+        _logger.LogInformation("Notifying sprint {SprintId} updated", sprintId);
+
+        await _projectHubContext.Clients.Group(projectGroupName).SendAsync("SprintUpdated", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+    }
+
+    public async Task NotifySprintStarted(Guid tenantId, Guid projectId, Guid sprintId, string sprintName)
+    {
+        var projectGroupName = $"project-{projectId}";
+        var tenantGroupName = $"tenant-{tenantId}";
+
+        _logger.LogInformation("Notifying sprint {SprintId} started", sprintId);
+
+        await _projectHubContext.Clients.Group(projectGroupName).SendAsync("SprintStarted", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+
+        await _projectHubContext.Clients.Group(tenantGroupName).SendAsync("SprintStarted", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+    }
+
+    public async Task NotifySprintCompleted(Guid tenantId, Guid projectId, Guid sprintId, string sprintName)
+    {
+        var projectGroupName = $"project-{projectId}";
+        var tenantGroupName = $"tenant-{tenantId}";
+
+        _logger.LogInformation("Notifying sprint {SprintId} completed", sprintId);
+
+        await _projectHubContext.Clients.Group(projectGroupName).SendAsync("SprintCompleted", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+
+        await _projectHubContext.Clients.Group(tenantGroupName).SendAsync("SprintCompleted", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+    }
+
+    public async Task NotifySprintDeleted(Guid tenantId, Guid projectId, Guid sprintId, string sprintName)
+    {
+        var projectGroupName = $"project-{projectId}";
+        var tenantGroupName = $"tenant-{tenantId}";
+
+        _logger.LogInformation("Notifying sprint {SprintId} deleted", sprintId);
+
+        await _projectHubContext.Clients.Group(projectGroupName).SendAsync("SprintDeleted", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+
+        await _projectHubContext.Clients.Group(tenantGroupName).SendAsync("SprintDeleted", new
+        {
+            SprintId = sprintId,
+            SprintName = sprintName,
+            ProjectId = projectId,
+            Timestamp = DateTime.UtcNow
+        });
+    }
+
     public async Task NotifyUser(Guid userId, string message, string type = "info")
     {
         var userConnectionId = $"user-{userId}";