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/includes/AuditLog.php

@@ -460,7 +460,9 @@ class AuditLog
 
             // Get logs
             $sql = "
-                SELECT *
+                SELECT id, user_id, username, user_ip, action,
+                       entity_type, entity_id, description,
+                       old_values, new_values, created_at
                 FROM audit_logs
                 $whereClause
                 ORDER BY created_at DESC
@@ -503,7 +505,9 @@ class AuditLog
             $pdo = db();
 
             $stmt = $pdo->prepare('
-                SELECT *
+                SELECT id, user_id, username, user_ip, action,
+                       entity_type, entity_id, description,
+                       old_values, new_values, created_at
                 FROM audit_logs
                 WHERE user_id = ?
                 ORDER BY created_at DESC
@@ -531,7 +535,9 @@ class AuditLog
             $pdo = db();
 
             $stmt = $pdo->prepare('
-                SELECT *
+                SELECT id, user_id, username, user_ip, action,
+                       entity_type, entity_id, description,
+                       old_values, new_values, created_at
                 FROM audit_logs
                 WHERE entity_type = ? AND entity_id = ?
                 ORDER BY created_at DESC