refactor: sjednoceni zdroje casu na MySQL NOW() + audit log cleanup a UI

- attendance handlery pouzivaji getDbNow() misto PHP date()
- nova helper funkce getDbNow() v AttendanceHelpers.php
- audit log: cleanup endpoint (POST) s volbou stari zaznamu
- audit log: filtry na jednom radku
- dashboard: aktivita prejmenovana na Audit log s odkazem

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

api/admin/audit-log.php

@@ -26,12 +26,44 @@ if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
     exit;
 }
 
-if ($_SERVER['REQUEST_METHOD'] !== 'GET') {
+if (!in_array($_SERVER['REQUEST_METHOD'], ['GET', 'POST'], true)) {
     errorResponse('Method not allowed', 405);
 }
 
 requirePermission($authData, 'settings.audit');
 
+if ($_SERVER['REQUEST_METHOD'] === 'POST') {
+    $input = getJsonInput();
+    $action = $input['action'] ?? '';
+
+    if ($action !== 'cleanup') {
+        errorResponse('Neplatná akce');
+    }
+
+    $days = (int) ($input['days'] ?? 90);
+    $pdo = db();
+
+    if ($days === 0) {
+        $stmt = $pdo->query('DELETE FROM audit_logs');
+        $deleted = $stmt->rowCount();
+        $msg = $deleted > 0
+            ? "Smazáno všech $deleted záznamů"
+            : 'Audit log je prázdný';
+    } else {
+        $days = max(1, $days);
+        $stmt = $pdo->prepare(
+            'DELETE FROM audit_logs WHERE created_at < DATE_SUB(NOW(), INTERVAL ? DAY)'
+        );
+        $stmt->execute([$days]);
+        $deleted = $stmt->rowCount();
+        $msg = $deleted > 0
+            ? "Smazáno $deleted záznamů starších $days dní"
+            : "Žádné záznamy starší než $days dní nebyly nalezeny";
+    }
+
+    successResponse(['deleted' => $deleted], $msg);
+}
+
 $page = max(1, (int) ($_GET['page'] ?? 1));
 $perPage = max(1, min(100, (int) ($_GET['per_page'] ?? 50)));