Add PHP 7.4+ type hints to helpers, models, and middleware

Added strict typing with parameter types, return types, and property
types across all core classes:
- helpers: Database, ErrorHandler, CacheHelper
- models: TicketModel, UserModel, WorkflowModel, TemplateModel, UserPreferencesModel
- middleware: RateLimitMiddleware, CsrfMiddleware, SecurityHeadersMiddleware

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

models/UserPreferencesModel.php

@@ -6,11 +6,11 @@
 require_once dirname(__DIR__) . '/helpers/CacheHelper.php';
 
 class UserPreferencesModel {
-    private $conn;
-    private static $CACHE_PREFIX = 'user_prefs';
-    private static $CACHE_TTL = 300; // 5 minutes
+    private mysqli $conn;
+    private static string $CACHE_PREFIX = 'user_prefs';
+    private static int $CACHE_TTL = 300; // 5 minutes
 
-    public function __construct($conn) {
+    public function __construct(mysqli $conn) {
         $this->conn = $conn;
     }
 
@@ -19,7 +19,7 @@ class UserPreferencesModel {
      * @param int $userId User ID
      * @return array Associative array of preference_key => preference_value
      */
-    public function getUserPreferences($userId) {
+    public function getUserPreferences(int $userId): array {
         return CacheHelper::remember(self::$CACHE_PREFIX, $userId, function() use ($userId) {
             $sql = "SELECT preference_key, preference_value
                     FROM user_preferences
@@ -45,7 +45,7 @@ class UserPreferencesModel {
      * @param string $value Preference value
      * @return bool Success status
      */
-    public function setPreference($userId, $key, $value) {
+    public function setPreference(int $userId, string $key, string $value): bool {
         $sql = "INSERT INTO user_preferences (user_id, preference_key, preference_value)
                 VALUES (?, ?, ?)
                 ON DUPLICATE KEY UPDATE preference_value = VALUES(preference_value)";
@@ -69,7 +69,7 @@ class UserPreferencesModel {
      * @param mixed $default Default value if preference doesn't exist
      * @return mixed Preference value or default
      */
-    public function getPreference($userId, $key, $default = null) {
+    public function getPreference(int $userId, string $key, $default = null) {
         $prefs = $this->getUserPreferences($userId);
         return $prefs[$key] ?? $default;
     }
@@ -80,7 +80,7 @@ class UserPreferencesModel {
      * @param string $key Preference key
      * @return bool Success status
      */
-    public function deletePreference($userId, $key) {
+    public function deletePreference(int $userId, string $key): bool {
         $sql = "DELETE FROM user_preferences
                 WHERE user_id = ? AND preference_key = ?";
         $stmt = $this->conn->prepare($sql);
@@ -101,7 +101,7 @@ class UserPreferencesModel {
      * @param int $userId User ID
      * @return bool Success status
      */
-    public function deleteAllPreferences($userId) {
+    public function deleteAllPreferences(int $userId): bool {
         $sql = "DELETE FROM user_preferences WHERE user_id = ?";
         $stmt = $this->conn->prepare($sql);
         $stmt->bind_param("i", $userId);
@@ -119,7 +119,7 @@ class UserPreferencesModel {
     /**
      * Clear all user preferences cache
      */
-    public static function clearCache() {
+    public static function clearCache(): void {
         CacheHelper::delete(self::$CACHE_PREFIX);
     }
 }