Add PostgreSQL-backed data storage support (#444)

Co-authored-by: samanhappy <samanhappy@gmail.com>

.env.example

@@ -1,2 +1,8 @@
 PORT=3000
 NODE_ENV=development
+
+# Database Configuration (Optional - for database-backed configuration)
+# Simply set DB_URL to enable database mode (auto-detected)
+# DB_URL=postgresql://mcphub:password@localhost:5432/mcphub
+# Or explicitly control with USE_DB (overrides auto-detection)
+# USE_DB=true