Fix: Critical API and dark mode issues

Fixed multiple critical issues reported by user:

1. **API Configuration Errors:**
   - Fixed all API files to use correct config path (config/config.php instead of config/db.php)
   - Fixed: get_users.php (bulk assign dropdown now loads users)
   - Fixed: get_template.php (templates now load correctly)
   - Fixed: bulk_operation.php (bulk operations now work)
   - Fixed: assign_ticket.php (manual assignment now works)

2. **Dark Mode Improvements:**
   - Added dark mode support for Activity tab content
   - Ensured proper text and background colors in dark mode

All APIs now properly:
- Load configuration from config/config.php
- Use correct session variables ($_SESSION['user']['user_id'])
- Create and close database connections properly
- Return proper JSON responses

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

api/assign_ticket.php

@@ -1,6 +1,6 @@
 <?php
 session_start();
-require_once dirname(__DIR__) . '/config/db.php';
+require_once dirname(__DIR__) . '/config/config.php';
 require_once dirname(__DIR__) . '/models/TicketModel.php';
 require_once dirname(__DIR__) . '/models/AuditLogModel.php';