feat: Daily+hatchet default (#846)

* feat: set Daily as default video platform

Daily.co has been battle-tested and is ready to be the default.
Whereby remains available for rooms that explicitly set it.

* feat: enforce Hatchet for all multitrack processing

Remove use_celery option from rooms - multitrack (Daily) recordings
now always use Hatchet workflows. Celery remains for single-track
(Whereby) file processing only.

- Remove use_celery column from room table
- Simplify dispatch logic to always use Hatchet for multitracks
- Update tests to mock Hatchet instead of Celery

* fix: update whereby test to patch Hatchet instead of removed Celery import

---------

Co-authored-by: Igor Loskutov <igor.loskutoff@gmail.com>

server/tests/conftest.py

@@ -4,7 +4,7 @@ from unittest.mock import patch
 
 import pytest
 
-from reflector.schemas.platform import WHEREBY_PLATFORM
+from reflector.schemas.platform import DAILY_PLATFORM, WHEREBY_PLATFORM
 
 
 @pytest.fixture(scope="session", autouse=True)
@@ -14,6 +14,7 @@ def register_mock_platform():
     from reflector.video_platforms.registry import register_platform
 
     register_platform(WHEREBY_PLATFORM, MockPlatformClient)
+    register_platform(DAILY_PLATFORM, MockPlatformClient)
     yield