[video-engine] Per-project video_engine_enabled opt-in toggle

Mirrors ci_watch_enabled (migration 048): the global
ROBOCO_VIDEO_ENGINE_ENABLED flag arms the subsystem; the new
projects.video_engine_enabled column (migration 063) opts a repo into
authoring against its motion/ dir. VideoEngine._opted_in_project no-ops
open_video_task at the single chokepoint covering all three trigger
paths (on-release, on-spotlight, CEO on-demand) until the operator
flips it in the panel edit-project dialog. Existing projects stay
opted out (server_default=false).

tests/unit/services/test_video_engine.py

@@ -72,6 +72,7 @@ async def _seed(session: AsyncSession) -> None:
                 assigned_cell=Team.BACKEND,
                 created_by=SYSTEM_UUID,
                 is_active=True,
+                video_engine_enabled=True,
             )
         )
     await session.flush()
@@ -214,6 +215,27 @@ async def test_open_video_task_unresolvable_project_opens_nothing(
     assert await get_task_service(db_session).list_open_video_posts() == []
 
 
+@pytest.mark.asyncio
+async def test_open_video_task_no_op_when_project_not_opted_in(
+    db_session: AsyncSession, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    await _seed(db_session)
+    # Flip the per-project opt-in back off — the global flag stays on.
+    await db_session.execute(
+        ProjectTable.__table__.update()
+        .where(ProjectTable.__table__.c.slug == SLUG)
+        .values(video_engine_enabled=False)
+    )
+    await db_session.flush()
+    _enable(monkeypatch)
+    engine = video_engine_module.VideoEngine(db_session)
+    task = await engine.open_video_task(
+        occasion="release v1.0.0", script="s", platforms=["x"], brief="b"
+    )
+    assert task is None
+    assert await get_task_service(db_session).list_open_video_posts() == []
+
+
 @pytest.mark.asyncio
 async def test_open_video_task_insert_error_returns_none_session_usable(
     db_session: AsyncSession, monkeypatch: pytest.MonkeyPatch
@@ -255,6 +277,7 @@ async def test_open_video_task_insert_error_returns_none_session_usable(
                 assigned_cell=Team.BACKEND,
                 created_by=SYSTEM_UUID,
                 is_active=True,
+                video_engine_enabled=True,
             )
         )
     await db_session.flush()