feat(music-lab): pipeline 5개 DB 테이블 + 헬퍼

YouTube 음악 파이프라인 Task 1 — 신규 5개 테이블과 헬퍼 함수 추가.

테이블:
- video_pipelines: 파이프라인 단위 상태 머신 + 메타/리뷰 JSON
- pipeline_jobs: 단계별 비동기 작업 상태/시간
- pipeline_feedback: 텔레그램 피드백 이력
- youtube_oauth_tokens: 채널 OAuth refresh/access 토큰
- youtube_setup: 단일 행 설정 (메타 템플릿/커버 프롬프트/리뷰 가중치/임계값/비주얼/공개정책)

헬퍼:
- create_pipeline / get_pipeline / update_pipeline_state / list_pipelines
- increment_feedback_count / record_feedback / get_feedback_history
- create_pipeline_job / update_pipeline_job / list_pipeline_jobs
- get_youtube_setup / update_youtube_setup
- upsert_oauth_token / get_oauth_token / delete_oauth_token

테스트:
- tests/test_pipeline_db.py: 7개 테스트 (생성/상태/피드백/잡/셋업/OAuth)
- tests/conftest.py: freezegun 기반 freezer fixture 추가
- requirements.txt: freezegun>=1.4 추가

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

music-lab/tests/conftest.py

@@ -1,7 +1,36 @@
 import pytest
 
+
 @pytest.fixture
 def tmp_db(tmp_path, monkeypatch):
     db_path = str(tmp_path / "test_music.db")
     monkeypatch.setattr("app.db.DB_PATH", db_path)
     return db_path
+
+
+@pytest.fixture
+def freezer():
+    """Minimal freezegun-based fixture providing `move_to(time)` to mimic
+    pytest-freezer's `freezer` fixture using only the `freezegun` package."""
+    from freezegun import freeze_time
+
+    class _Freezer:
+        def __init__(self):
+            self._ctx = None
+
+        def move_to(self, target):
+            if self._ctx is not None:
+                self._ctx.stop()
+            self._ctx = freeze_time(target)
+            self._ctx.start()
+
+        def stop(self):
+            if self._ctx is not None:
+                self._ctx.stop()
+                self._ctx = None
+
+    f = _Freezer()
+    try:
+        yield f
+    finally:
+        f.stop()