fix(backend): Fix Integration Test database provider conflict with environment-aware DI

Implement environment-aware dependency injection to resolve EF Core provider conflict
in Integration Tests. The issue was caused by both PostgreSQL and InMemory providers
being registered in the same service provider.

Changes:
- Modified Identity Module DependencyInjection to skip PostgreSQL DbContext registration in Testing environment
- Modified ProjectManagement Module ModuleExtensions with same environment check
- Updated Program.cs to pass IHostEnvironment to both module registration methods
- Added Microsoft.Extensions.Hosting.Abstractions package to Identity.Infrastructure project
- Updated ColaFlowWebApplicationFactory to set Testing environment and register InMemory databases
- Simplified WebApplicationFactory by removing complex RemoveAll logic

Results:
- All 31 Integration Tests now run (previously only 1 ran)
- No EF Core provider conflict errors
- 23 tests pass, 8 tests fail (failures are business logic issues, not infrastructure)
- Production environment still uses PostgreSQL as expected

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

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

colaflow-api/src/ColaFlow.API/Extensions/ModuleExtensions.cs

@@ -6,6 +6,7 @@ using ColaFlow.Modules.ProjectManagement.Application.Commands.CreateProject;
 using ColaFlow.Modules.ProjectManagement.Domain.Repositories;
 using ColaFlow.Modules.ProjectManagement.Infrastructure.Persistence;
 using ColaFlow.Modules.ProjectManagement.Infrastructure.Repositories;
+using Microsoft.Extensions.Hosting;
 
 namespace ColaFlow.API.Extensions;
 
@@ -19,12 +20,18 @@ public static class ModuleExtensions
     /// </summary>
     public static IServiceCollection AddProjectManagementModule(
         this IServiceCollection services,
-        IConfiguration configuration)
+        IConfiguration configuration,
+        IHostEnvironment? environment = null)
     {
-        // Register DbContext
-        var connectionString = configuration.GetConnectionString("PMDatabase");
-        services.AddDbContext<PMDbContext>(options =>
-            options.UseNpgsql(connectionString));
+        // Only register PostgreSQL DbContext in non-Testing environments
+        // In Testing environment, WebApplicationFactory will register InMemory provider
+        if (environment == null || environment.EnvironmentName != "Testing")
+        {
+            // Register DbContext
+            var connectionString = configuration.GetConnectionString("PMDatabase");
+            services.AddDbContext<PMDbContext>(options =>
+                options.UseNpgsql(connectionString));
+        }
 
         // Register repositories
         services.AddScoped<IProjectRepository, ProjectRepository>();