Replace ZipStream with native ZipArchive for FrankenPHP compatibility

ZipStream writes via fwrite(php://output) which FrankenPHP silently
drops, resulting in 0-byte ZIP downloads. Switch to ZipArchive to build
the ZIP as a temp file on disk, then serve with response()->download().

- Rewrite download() to use ZipArchive + BinaryFileResponse
- Remove decryptFileToCallback() from FileEncryptionService
- Update tests for BinaryFileResponse instead of StreamedResponse
- Remove maennchen/zipstream-php dependency

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

composer.json

@@ -15,7 +15,6 @@
         "laravel/octane": "^2.13",
         "laravel/tinker": "^2.10.1",
         "livewire/livewire": "^4.0",
-        "maennchen/zipstream-php": "^3.2",
         "robsontenorio/mary": "^2.7"
     },
     "require-dev": {