Audit fixes: security, dead code removal, API consolidation, JS dedup

Security:
- Fix IDOR in delete/update comment (add ticket visibility check)
- XSS defense-in-depth in DashboardView active filters
- Replace innerHTML with DOM construction in toast.js
- Remove redundant real_escape_string in check_duplicates
- Add rate limiting to get_template, download_attachment, audit_log,
  saved_filters, user_preferences endpoints

Bug fixes:
- Session timeout now reads from config instead of hardcoded 18000
- TicketController uses $GLOBALS['config'] instead of duplicate .env parsing
- Add DISCORD_WEBHOOK_URL to centralized config
- Cleanup script uses hashmap for O(1) ticket ID lookups

Dead code removal (~100 lines):
- Remove dead getTicketComments() from TicketModel (wrong bind_param type)
- Remove dead getCategories()/getTypes() from DashboardController
- Remove ~80 lines dead Discord webhook code from update_ticket API

Consolidation:
- Create api/bootstrap.php for shared API setup (auth, CSRF, rate limit)
- Convert 6 API endpoints to use bootstrap
- Extract escapeHtml/getTicketIdFromUrl into shared utils.js
- Batch save for user preferences (1 request instead of 7)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

api/assign_ticket.php

@@ -1,36 +1,9 @@
 <?php
-// Apply rate limiting
-require_once dirname(__DIR__) . '/middleware/RateLimitMiddleware.php';
-RateLimitMiddleware::apply('api');
-
-session_start();
-require_once dirname(__DIR__) . '/config/config.php';
-require_once dirname(__DIR__) . '/helpers/Database.php';
+require_once __DIR__ . '/bootstrap.php';
 require_once dirname(__DIR__) . '/models/TicketModel.php';
 require_once dirname(__DIR__) . '/models/AuditLogModel.php';
 require_once dirname(__DIR__) . '/models/UserModel.php';
 
-header('Content-Type: application/json');
-
-// Check authentication
-if (!isset($_SESSION['user']) || !isset($_SESSION['user']['user_id'])) {
-    echo json_encode(['success' => false, 'error' => 'Not authenticated']);
-    exit;
-}
-
-// CSRF Protection
-require_once dirname(__DIR__) . '/middleware/CsrfMiddleware.php';
-if ($_SERVER['REQUEST_METHOD'] === 'POST') {
-    $csrfToken = $_SERVER['HTTP_X_CSRF_TOKEN'] ?? '';
-    if (!CsrfMiddleware::validateToken($csrfToken)) {
-        http_response_code(403);
-        echo json_encode(['success' => false, 'error' => 'Invalid CSRF token']);
-        exit;
-    }
-}
-
-$userId = $_SESSION['user']['user_id'];
-
 // Get request data
 $data = json_decode(file_get_contents('php://input'), true);
 $ticketId = $data['ticket_id'] ?? null;
@@ -41,9 +14,6 @@ if (!$ticketId) {
     exit;
 }
 
-// Use centralized database connection
-$conn = Database::getConnection();
-
 $ticketModel = new TicketModel($conn);
 $auditLogModel = new AuditLogModel($conn);
 $userModel = new UserModel($conn);