feat: filemanager s NAS pro projekty

- NasFileManager.php - filesystem helper (browse, upload, download, delete, rename, mkdir)
- project-files.php API - CRUD operace nad soubory projektu
- ProjectFileManager.jsx - React komponenta v detailu projektu
- Automaticke vytvoreni slozky pri vytvoreni projektu (rucne i z objednavky)
- Prejmenovani slozky pri zmene nazvu projektu
- Checkbox "Smazat i soubory na disku" pri mazani projektu/objednavky
- Path traversal ochrana, MIME validace, blocklist nebezpecnych typu
- Bily spinner v primary tlacitkach, ConfirmModal message jako div
- Case-insensitive rename fix pro Windows filesystem

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

dist/api/includes/constants.php

@@ -36,3 +36,12 @@ define('INCLUDES_PATH', API_ROOT . '/includes');
 
 // Rate limiting
 define('RATE_LIMIT_STORAGE_PATH', dirname(__DIR__) . '/rate_limits');
+
+// NAS File Manager
+define('NAS_FILES_PATH', env('NAS_FILES_PATH', ''));
+define('NAS_MAX_UPLOAD_SIZE', (int) env('NAS_MAX_UPLOAD_SIZE', 52428800));
+define(
+    'NAS_ALLOWED_EXTENSIONS',
+    array_filter(array_map('trim', explode(',', (string) env('NAS_ALLOWED_EXTENSIONS', ''))))
+);
+define('NAS_BLOCKED_EXTENSIONS', ['exe', 'bat', 'sh', 'php', 'htaccess', 'env', 'cmd', 'com', 'msi', 'ps1']);