feat(backend): Implement complete RBAC system (Day 5 Phase 2)

Implemented Role-Based Access Control (RBAC) with 5 tenant-level roles following Clean Architecture principles.

Changes:
- Created TenantRole enum (TenantOwner, TenantAdmin, TenantMember, TenantGuest, AIAgent)
- Created UserTenantRole entity with repository pattern
- Updated JWT service to include role claims (tenant_role, role)
- Updated RegisterTenant to auto-assign TenantOwner role
- Updated Login to query and include user role in JWT
- Updated RefreshToken to preserve role claims
- Added authorization policies in Program.cs (RequireTenantOwner, RequireTenantAdmin, etc.)
- Updated /api/auth/me endpoint to return role information
- Created EF Core migration for user_tenant_roles table
- Applied database migration successfully

Database:
- New table: identity.user_tenant_roles
- Columns: id, user_id, tenant_id, role, assigned_at, assigned_by_user_id
- Indexes: user_id, tenant_id, role, unique(user_id, tenant_id)
- Foreign keys: CASCADE on user and tenant deletion

Testing:
- Created test-rbac.ps1 PowerShell script
- All RBAC tests passing
- JWT tokens contain role claims
- Role persists across login and token refresh

Documentation:
- DAY5-PHASE2-RBAC-IMPLEMENTATION-SUMMARY.md with complete implementation details

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

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

colaflow-api/src/Modules/Identity/ColaFlow.Modules.Identity.Infrastructure/DependencyInjection.cs

@@ -29,6 +29,7 @@ public static class DependencyInjection
         services.AddScoped<ITenantRepository, TenantRepository>();
         services.AddScoped<IUserRepository, UserRepository>();
         services.AddScoped<IRefreshTokenRepository, RefreshTokenRepository>();
+        services.AddScoped<IUserTenantRoleRepository, UserTenantRoleRepository>();
 
         // Application Services
         services.AddScoped<IJwtService, JwtService>();