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/customers-handlers.php

@@ -54,7 +54,9 @@ function encodeCustomerCustomFields(array $input, ?string $existingJson): ?strin
 function handleGetAll(PDO $pdo): void
 {
     $stmt = $pdo->query('
-        SELECT c.*, COUNT(q.id) as quotation_count
+        SELECT c.id, c.name, c.street, c.city, c.postal_code, c.country,
+               c.company_id, c.vat_id, c.custom_fields, c.created_at,
+               COUNT(q.id) as quotation_count
         FROM customers c
         LEFT JOIN quotations q ON q.customer_id = c.id
         GROUP BY c.id
@@ -72,7 +74,11 @@ function handleGetAll(PDO $pdo): void
 
 function handleGetOne(PDO $pdo, int $id): void
 {
-    $stmt = $pdo->prepare('SELECT * FROM customers WHERE id = ?');
+    $stmt = $pdo->prepare(
+        'SELECT id, name, street, city, postal_code, country,
+                company_id, vat_id, custom_fields, created_at
+        FROM customers WHERE id = ?'
+    );
     $stmt->execute([$id]);
     $customer = $stmt->fetch();
 
@@ -93,7 +99,9 @@ function handleSearch(PDO $pdo): void
     }
 
     $stmt = $pdo->prepare('
-        SELECT * FROM customers
+        SELECT id, name, street, city, postal_code, country,
+               company_id, vat_id, custom_fields
+        FROM customers
         WHERE name LIKE ? OR company_id LIKE ? OR city LIKE ?
         ORDER BY name ASC
         LIMIT 20
@@ -177,7 +185,11 @@ function handleCreateCustomer(PDO $pdo): void
 
 function handleUpdateCustomer(PDO $pdo, int $id): void
 {
-    $stmt = $pdo->prepare('SELECT * FROM customers WHERE id = ?');
+    $stmt = $pdo->prepare(
+        'SELECT id, name, street, city, postal_code, country,
+                company_id, vat_id, custom_fields
+        FROM customers WHERE id = ?'
+    );
     $stmt->execute([$id]);
     $existing = $stmt->fetch();
 
@@ -248,7 +260,7 @@ function handleUpdateCustomer(PDO $pdo, int $id): void
 
 function handleDeleteCustomer(PDO $pdo, int $id): void
 {
-    $stmt = $pdo->prepare('SELECT * FROM customers WHERE id = ?');
+    $stmt = $pdo->prepare('SELECT id, name FROM customers WHERE id = ?');
     $stmt->execute([$id]);
     $customer = $stmt->fetch();