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/knexfile.js

@@ -40,10 +40,10 @@ const config = {
       keepAliveInitialDelayMillis: 0
     },
     pool: {
-      min: 2,
-      max: 10,
-      acquireTimeoutMillis: 30000,
-      createTimeoutMillis: 30000,
+      min: 5,
+      max: 25,
+      acquireTimeoutMillis: 60000,
+      createTimeoutMillis: 60000,
       idleTimeoutMillis: 30000,
       reapIntervalMillis: 1000,
       createRetryIntervalMillis: 200,