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/Database.php

@@ -6,7 +6,7 @@
  * Provides a singleton connection for the request lifecycle.
  */
 class Database {
-    private static $connection = null;
+    private static ?mysqli $connection = null;
 
     /**
      * Get database connection (singleton pattern)
@@ -14,7 +14,7 @@ class Database {
      * @return mysqli Database connection
      * @throws Exception If connection fails
      */
-    public static function getConnection() {
+    public static function getConnection(): mysqli {
         if (self::$connection === null) {
             self::$connection = self::createConnection();
         }
@@ -33,7 +33,7 @@ class Database {
      * @return mysqli Database connection
      * @throws Exception If connection fails
      */
-    private static function createConnection() {
+    private static function createConnection(): mysqli {
         // Ensure config is loaded
         if (!isset($GLOBALS['config'])) {
             require_once dirname(__DIR__) . '/config/config.php';
@@ -59,7 +59,7 @@ class Database {
     /**
      * Close the database connection
      */
-    public static function close() {
+    public static function close(): void {
         if (self::$connection !== null) {
             self::$connection->close();
             self::$connection = null;
@@ -71,7 +71,7 @@ class Database {
      *
      * @return bool Success
      */
-    public static function beginTransaction() {
+    public static function beginTransaction(): bool {
         return self::getConnection()->begin_transaction();
     }
 
@@ -80,7 +80,7 @@ class Database {
      *
      * @return bool Success
      */
-    public static function commit() {
+    public static function commit(): bool {
         return self::getConnection()->commit();
     }
 
@@ -89,7 +89,7 @@ class Database {
      *
      * @return bool Success
      */
-    public static function rollback() {
+    public static function rollback(): bool {
         return self::getConnection()->rollback();
     }
 
@@ -101,7 +101,7 @@ class Database {
      * @param array $params Parameters to bind
      * @return mysqli_result|bool Query result
      */
-    public static function query($sql, $types = '', $params = []) {
+    public static function query(string $sql, string $types = '', array $params = []) {
         $conn = self::getConnection();
 
         if (empty($types) || empty($params)) {
@@ -130,7 +130,7 @@ class Database {
      * @param array $params Parameters to bind
      * @return int Affected rows (-1 on failure)
      */
-    public static function execute($sql, $types = '', $params = []) {
+    public static function execute(string $sql, string $types = '', array $params = []): int {
         $conn = self::getConnection();
 
         $stmt = $conn->prepare($sql);
@@ -158,7 +158,7 @@ class Database {
      *
      * @return int Last insert ID
      */
-    public static function lastInsertId() {
+    public static function lastInsertId(): int {
         return self::getConnection()->insert_id;
     }
 
@@ -168,7 +168,7 @@ class Database {
      * @param string $string String to escape
      * @return string Escaped string
      */
-    public static function escape($string) {
+    public static function escape(string $string): string {
         return self::getConnection()->real_escape_string($string);
     }
 }