feat: Add 9 new features for enhanced UX and security

Quick Wins:
- Feature 1: Ticket linking in comments (#123456789 auto-links)
- Feature 6: Checkbox click area fix (click anywhere in cell)
- Feature 7: User groups display in settings modal

UI Enhancements:
- Feature 4: Collapsible sidebar with localStorage persistence
- Feature 5: Inline ticket preview popup on hover (300ms delay)
- Feature 2: Mobile responsive improvements (44px touch targets, iOS zoom fix)

Major Features:
- Feature 3: Kanban card view with status columns (toggle with localStorage)
- Feature 9: API key generation admin panel (/admin/api-keys)
- Feature 8: Ticket visibility levels (public/internal/confidential)

New files:
- views/admin/ApiKeysView.php
- api/generate_api_key.php
- api/revoke_api_key.php
- migrations/008_ticket_visibility.sql

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

api/update_ticket.php

@@ -144,6 +144,16 @@ try {
             // Update ticket with user tracking
             $result = $this->ticketModel->updateTicket($updateData, $this->userId);
 
+            // Handle visibility update if provided
+            if ($result && isset($data['visibility'])) {
+                $visibilityGroups = $data['visibility_groups'] ?? null;
+                // Convert array to comma-separated string if needed
+                if (is_array($visibilityGroups)) {
+                    $visibilityGroups = implode(',', array_map('trim', $visibilityGroups));
+                }
+                $this->ticketModel->updateVisibility($id, $data['visibility'], $visibilityGroups, $this->userId);
+            }
+
             if ($result) {
                 // Log ticket update to audit log
                 if ($this->userId) {