update env setup

backend/src/config/environment.ts

@@ -1,12 +1,9 @@
 import dotenv from 'dotenv';
 import path from 'path';
 
-// Load environment-specific .env file
-const envFile = process.env.NODE_ENV === 'production'
-  ? '.env.production'
-  : '.env.development';
-
-dotenv.config({ path: path.resolve(__dirname, '../../', envFile) });
+// Load from root .env (project-wide single source of truth).
+// In Docker, env vars are already injected by docker-compose so this is a no-op.
+dotenv.config({ path: path.resolve(__dirname, '../../../.env') });
 
 interface EnvironmentConfig {
   nodeEnv: string;