fix: critical database connection pool exhaustion issues

- Disabled duplicate email service (emailService.js) that was creating redundant connections
- Increased connection pool size from 10 to 25 for production environment
- Extended session timeout cache from 5 to 30 minutes to reduce DB queries
- Added connection retry logic with exponential backoff for transient failures
- Fixed password validation to use retry wrapper and correct setting key
- Updated public settings and gallery middleware to handle connection failures gracefully

These changes address the "Connection terminated unexpectedly" errors in production by:
1. Reducing unnecessary database connections
2. Increasing available connection pool capacity
3. Implementing automatic retry for transient connection failures
4. Caching frequently accessed data for longer periods

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

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

backend/src/middleware/sessionTimeout.js

@@ -10,7 +10,7 @@ const DEFAULT_SESSION_TIMEOUT = 60 * 60 * 1000;
 // Cache for session timeout setting
 let cachedTimeout = null;
 let cacheExpiry = 0;
-const CACHE_DURATION = 5 * 60 * 1000; // 5 minutes
+const CACHE_DURATION = 30 * 60 * 1000; // 30 minutes - reduced DB queries
 
 // Clean up expired sessions every 5 minutes
 setInterval(() => {