fix: multiple production issues with PostgreSQL and connection handling

- Fix trust proxy to use specific values instead of permissive 'true'
- Fix clear old notifications to use database-agnostic date calculation
- Fix database size check to support both PostgreSQL and SQLite
- Add caching and better error handling for session timeout queries
- Add query timeout to prevent hanging connections
- Improve JSON parsing error handling for setting values

These fixes address:
- ERR_ERL_PERMISSIVE_TRUST_PROXY warning
- PostgreSQL datetime function errors
- ENOENT errors looking for SQLite file in PostgreSQL deployment
- Connection terminated errors for session timeout checks

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

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

backend/src/routes/adminNotifications.js

@@ -100,9 +100,13 @@ router.put('/read-all', adminAuth, async (req, res) => {
 // Delete old notifications (older than 30 days and read)
 router.delete('/clear-old', adminAuth, async (req, res) => {
   try {
+    // Use database-agnostic date calculation
+    const thirtyDaysAgo = new Date();
+    thirtyDaysAgo.setDate(thirtyDaysAgo.getDate() - 30);
+    
     const deletedCount = await db('activity_logs')
       .whereNotNull('read_at')
-      .where('created_at', '<', db.raw("datetime('now', '-30 days')"))
+      .where('created_at', '<', thirtyDaysAgo)
       .delete();
 
     res.json({