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/routes/publicSettings.js

@@ -1,5 +1,5 @@
 const express = require('express');
-const { db } = require('../database/db');
+const { db, withRetry } = require('../database/db');
 const router = express.Router();
 
 // Get public settings (branding and theme)
@@ -7,12 +7,14 @@ router.get('/', async (req, res) => {
   try {
     // Fetch branding, theme, general, and security settings
     // Note: We include analytics in the query but it might not exist yet
-    const settings = await db('app_settings')
-      .where(function() {
-        this.whereIn('setting_type', ['branding', 'theme', 'general', 'security', 'analytics'])
-          .orWhere('setting_key', 'like', 'analytics_%');
-      })
-      .select('setting_key', 'setting_value');
+    const settings = await withRetry(async () => {
+      return await db('app_settings')
+        .where(function() {
+          this.whereIn('setting_type', ['branding', 'theme', 'general', 'security', 'analytics'])
+            .orWhere('setting_key', 'like', 'analytics_%');
+        })
+        .select('setting_key', 'setting_value');
+    });
     
     // Convert to object format
     const settingsObject = {};