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>

helpers/CacheHelper.php

@@ -6,15 +6,15 @@
  * such as workflow rules, user preferences, and configuration data.
  */
 class CacheHelper {
-    private static $cacheDir = null;
-    private static $memoryCache = [];
+    private static ?string $cacheDir = null;
+    private static array $memoryCache = [];
 
     /**
      * Get the cache directory path
      *
      * @return string Cache directory path
      */
-    private static function getCacheDir() {
+    private static function getCacheDir(): string {
         if (self::$cacheDir === null) {
             self::$cacheDir = sys_get_temp_dir() . '/tinker_tickets_cache';
             if (!is_dir(self::$cacheDir)) {
@@ -31,7 +31,7 @@ class CacheHelper {
      * @param mixed $identifier Unique identifier
      * @return string Cache key
      */
-    private static function makeKey($prefix, $identifier = null) {
+    private static function makeKey(string $prefix, $identifier = null): string {
         $key = $prefix;
         if ($identifier !== null) {
             $key .= '_' . md5(serialize($identifier));
@@ -47,7 +47,7 @@ class CacheHelper {
      * @param int $ttl Time-to-live in seconds (default 300 = 5 minutes)
      * @return mixed|null Cached data or null if not found/expired
      */
-    public static function get($prefix, $identifier = null, $ttl = 300) {
+    public static function get(string $prefix, $identifier = null, int $ttl = 300) {
         $key = self::makeKey($prefix, $identifier);
 
         // Check memory cache first (fastest)
@@ -88,7 +88,7 @@ class CacheHelper {
      * @param mixed $data Data to cache
      * @return bool Success
      */
-    public static function set($prefix, $identifier, $data) {
+    public static function set(string $prefix, $identifier, $data): bool {
         $key = self::makeKey($prefix, $identifier);
         $cached = [
             'time' => time(),
@@ -110,7 +110,7 @@ class CacheHelper {
      * @param mixed $identifier Unique identifier (null to delete all with prefix)
      * @return bool Success
      */
-    public static function delete($prefix, $identifier = null) {
+    public static function delete(string $prefix, $identifier = null): bool {
         if ($identifier !== null) {
             $key = self::makeKey($prefix, $identifier);
             unset(self::$memoryCache[$key]);
@@ -140,7 +140,7 @@ class CacheHelper {
      *
      * @return bool Success
      */
-    public static function clearAll() {
+    public static function clearAll(): bool {
         self::$memoryCache = [];
 
         $files = glob(self::getCacheDir() . '/*.json');
@@ -160,7 +160,7 @@ class CacheHelper {
      * @param int $ttl Time-to-live in seconds
      * @return mixed Cached or freshly fetched data
      */
-    public static function remember($prefix, $identifier, $callback, $ttl = 300) {
+    public static function remember(string $prefix, $identifier, callable $callback, int $ttl = 300) {
         $data = self::get($prefix, $identifier, $ttl);
 
         if ($data === null) {
@@ -178,7 +178,7 @@ class CacheHelper {
      *
      * @param int $maxAge Maximum age in seconds (default 1 hour)
      */
-    public static function cleanup($maxAge = 3600) {
+    public static function cleanup(int $maxAge = 3600): void {
         $files = glob(self::getCacheDir() . '/*.json');
         $now = time();