feat: P4 backend kvalita - SELECT * fix, overdue konsolidace, Validator

- SELECT * nahrazen explicitnimi sloupci ve 22 PHP souborech (69+ vyskytu)
- users-handlers.php: password_hash explicitne vyloucen z dotazu
- Overdue detekce presunuta do invoices.php routeru (1x pred dispatch misto 3x v handlerech)
- Validator.php: validacni helper s pravidly required, string, int, email, in, numeric
- PaginationHelper: PHPStan typy opraveny

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

api/admin/handlers/roles-handlers.php

@@ -9,7 +9,8 @@ function handleGetRole(PDO $pdo): void
 {
     // Get all roles with user count (LEFT JOIN instead of correlated subquery)
     $stmt = $pdo->query('
-        SELECT r.*, COUNT(u.id) as user_count
+        SELECT r.id, r.name, r.display_name, r.description, r.created_at,
+               COUNT(u.id) as user_count
         FROM roles r
         LEFT JOIN users u ON u.role_id = r.id
         GROUP BY r.id
@@ -133,7 +134,9 @@ function handleCreateRole(PDO $pdo): void
 function handleUpdateRole(PDO $pdo, int $roleId): void
 {
     // Get existing role
-    $stmt = $pdo->prepare('SELECT * FROM roles WHERE id = ?');
+    $stmt = $pdo->prepare(
+        'SELECT id, name, display_name, description FROM roles WHERE id = ?'
+    );
     $stmt->execute([$roleId]);
     $role = $stmt->fetch();
 
@@ -205,7 +208,9 @@ function handleUpdateRole(PDO $pdo, int $roleId): void
  */
 function handleDeleteRole(PDO $pdo, int $roleId): void
 {
-    $stmt = $pdo->prepare('SELECT * FROM roles WHERE id = ?');
+    $stmt = $pdo->prepare(
+        'SELECT id, name, display_name, description FROM roles WHERE id = ?'
+    );
     $stmt->execute([$roleId]);
     $role = $stmt->fetch();