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/get_template.php

@@ -14,11 +14,14 @@ if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
 // Get template ID from query parameter
 $templateId = $_GET['template_id'] ?? null;
 
-if (!$templateId) {
-    echo json_encode(['success' => false, 'error' => 'Template ID required']);
+if (!$templateId || !is_numeric($templateId)) {
+    echo json_encode(['success' => false, 'error' => 'Valid template ID required']);
     exit;
 }
 
+// Cast to integer for safety
+$templateId = (int)$templateId;
+
 // Create database connection
 $conn = new mysqli(
     $GLOBALS['config']['DB_HOST'],