feat: Add admin navigation, fix modals, clickable stats, update docs

- Add admin dropdown menu in dashboard header with links to all admin pages
- Fix template modal: larger size (800px), responsive grid, type/priority dropdowns
- Fix recurring tickets modal: add Type and Assign To fields, larger size
- Make dashboard stat cards clickable for quick filtering
- Fix user-activity query (remove is_active requirement)
- Add table existence check in ticket_dependencies API
- Fix table overflow on dashboard
- Update Claude.md and README.md with current project status
- Remove migrations directory (all migrations completed)

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

index.php

@@ -224,7 +224,6 @@ switch (true) {
                     (SELECT COUNT(*) FROM tickets t WHERE t.assigned_to = u.user_id AND DATE(t.created_at) BETWEEN ? AND ?) as tickets_assigned,
                     (SELECT MAX(al.created_at) FROM audit_log al WHERE al.user_id = u.user_id) as last_activity
                 FROM users u
-                WHERE u.is_active = 1
                 ORDER BY tickets_created DESC, tickets_resolved DESC";
 
         $stmt = $conn->prepare($sql);