fix: database connection stability issues in production

- Add robust connection pool configuration with timeouts and retry settings
- Implement retry logic in maintenance middleware for connection errors
- Increase connection stability with keepAlive and proper timeout values
- Handle "Connection terminated unexpectedly" errors gracefully

This prevents 503 errors when the database connection is temporarily interrupted
and ensures the application can recover from transient connection issues.

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

Co-Authored-By: Claude <[email protected]>

backend/knexfile.js

@@ -32,15 +32,27 @@ const config = {
       user: process.env.DB_USER || 'picpeak',
       password: process.env.DB_PASSWORD,
       database: process.env.DB_NAME || 'picpeak',
-      ssl: process.env.DB_SSL === 'true' ? { rejectUnauthorized: false } : false
+      ssl: process.env.DB_SSL === 'true' ? { rejectUnauthorized: false } : false,
+      // Connection stability settings
+      connectionTimeoutMillis: 30000,
+      idleTimeoutMillis: 30000,
+      keepAlive: true,
+      keepAliveInitialDelayMillis: 0
     },
     pool: {
       min: 2,
-      max: 10
+      max: 10,
+      acquireTimeoutMillis: 30000,
+      createTimeoutMillis: 30000,
+      idleTimeoutMillis: 30000,
+      reapIntervalMillis: 1000,
+      createRetryIntervalMillis: 200,
+      propagateCreateError: false
     },
     migrations: {
       directory: './migrations'
-    }
+    },
+    acquireConnectionTimeout: 60000
   }
 };