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/Modules/Identity/ColaFlow.Modules.Identity.Infrastructure/DependencyInjection.cs

@@ -6,6 +6,7 @@ using ColaFlow.Modules.Identity.Infrastructure.Services;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
 
 namespace ColaFlow.Modules.Identity.Infrastructure;
 
@@ -13,13 +14,19 @@ public static class DependencyInjection
 {
     public static IServiceCollection AddIdentityInfrastructure(
         this IServiceCollection services,
-        IConfiguration configuration)
+        IConfiguration configuration,
+        IHostEnvironment? environment = null)
     {
-        // DbContext (using connection string)
-        services.AddDbContext<IdentityDbContext>(options =>
-            options.UseNpgsql(
-                configuration.GetConnectionString("DefaultConnection"),
-                b => b.MigrationsAssembly(typeof(IdentityDbContext).Assembly.FullName)));
+        // Only register PostgreSQL DbContext in non-Testing environments
+        // In Testing environment, WebApplicationFactory will register InMemory provider
+        if (environment == null || environment.EnvironmentName != "Testing")
+        {
+            // DbContext (using connection string)
+            services.AddDbContext<IdentityDbContext>(options =>
+                options.UseNpgsql(
+                    configuration.GetConnectionString("DefaultConnection"),
+                    b => b.MigrationsAssembly(typeof(IdentityDbContext).Assembly.FullName)));
+        }
 
         // Tenant Context (Scoped - one instance per request)
         services.AddScoped<ITenantContext, TenantContext>();