feat(backend): Implement PendingChange Management (Story 5.10)

Implemented complete Human-in-the-Loop approval workflow for AI-proposed changes:

Changes:
- Created PendingChange DTOs (PendingChangeDto, CreatePendingChangeRequest, ApproveChangeRequest, RejectChangeRequest, PendingChangeFilterDto)
- Implemented IPendingChangeService interface with CRUD, approval/rejection, expiration, and deletion operations
- Implemented PendingChangeService with full workflow support and tenant isolation
- Created McpPendingChangesController REST API with endpoints for listing, approving, rejecting, and deleting pending changes
- Implemented PendingChangeApprovedEventHandler to execute approved changes via MediatR commands (Project, Epic, Story, Task CRUD operations)
- Created PendingChangeExpirationBackgroundService for auto-expiration of changes after 24 hours
- Registered all services and background service in DI container

Technical Details:
- Status flow: PendingApproval → Approved → Applied (or Rejected/Expired)
- Tenant isolation enforced in all operations
- Domain events published for audit trail
- Event-driven execution using MediatR
- Background service runs every 5 minutes to expire old changes
- JWT authentication required for all endpoints

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

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

colaflow-api/src/Modules/Mcp/ColaFlow.Modules.Mcp.Infrastructure/Extensions/McpServiceExtensions.cs

@@ -3,6 +3,7 @@ using ColaFlow.Modules.Mcp.Application.Resources;
 using ColaFlow.Modules.Mcp.Application.Services;
 using ColaFlow.Modules.Mcp.Contracts.Resources;
 using ColaFlow.Modules.Mcp.Domain.Repositories;
+using ColaFlow.Modules.Mcp.Infrastructure.BackgroundServices;
 using ColaFlow.Modules.Mcp.Infrastructure.Middleware;
 using ColaFlow.Modules.Mcp.Infrastructure.Persistence;
 using ColaFlow.Modules.Mcp.Infrastructure.Persistence.Repositories;
@@ -41,6 +42,10 @@ public static class McpServiceExtensions
         services.AddScoped<ColaFlow.Modules.Mcp.Domain.Services.DiffPreviewService>();
         services.AddScoped<ColaFlow.Modules.Mcp.Domain.Services.TaskLockService>();
         services.AddScoped<IMcpApiKeyService, McpApiKeyService>();
+        services.AddScoped<IPendingChangeService, PendingChangeService>();
+
+        // Register background services
+        services.AddHostedService<PendingChangeExpirationBackgroundService>();
 
         // Register resource registry (Singleton - shared across all requests)
         services.AddSingleton<IMcpResourceRegistry, McpResourceRegistry>();