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>

assets/css/ticket.css

@@ -571,3 +571,17 @@ body.dark-mode .status-select option {
     background-color: #2d3748;
     color: #f7fafc;
 }
+
+/* Dark mode for Activity tab and general improvements */
+body.dark-mode .tab-content {
+    color: var(--text-primary, #f7fafc);
+}
+
+body.dark-mode #activity-tab {
+    background: var(--bg-secondary, #1a202c);
+    color: var(--text-primary, #f7fafc);
+}
+
+body.dark-mode #activity-tab p {
+    color: var(--text-primary, #f7fafc);
+}