Add automatic skip detection for playlist playback

Background poller monitors HA media_player state during playlist sessions.
When a track transition occurs and the previous track was played < 40% of
its duration, automatically records "skip" feedback. Also includes the
previously uncommitted delete_feedback endpoint.

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

src/haunt_fm/api/feedback.py

@@ -6,7 +6,7 @@ from sqlalchemy.orm import joinedload
 
 from haunt_fm.db import get_session
 from haunt_fm.models.track import FeedbackEvent, Track
-from haunt_fm.services.feedback import compute_contextual_score, record_feedback
+from haunt_fm.services.feedback import compute_contextual_score, delete_feedback, record_feedback
 
 router = APIRouter(prefix="/api/feedback")
 
@@ -41,6 +41,24 @@ async def submit_feedback(req: FeedbackRequest, session: AsyncSession = Depends(
     }
 
 
+@router.delete("/{event_id}")
+async def retract_feedback(event_id: int, session: AsyncSession = Depends(get_session)):
+    """Delete a feedback event entirely, removing its influence on scoring."""
+    event = await delete_feedback(session, event_id)
+    if event is None:
+        raise HTTPException(status_code=404, detail=f"Feedback event {event_id} not found")
+
+    return {
+        "id": event.id,
+        "playlist_id": event.playlist_id,
+        "track_id": event.track_id,
+        "signal": event.signal,
+        "signal_weight": event.signal_weight,
+        "vibe_text": event.vibe_text,
+        "created_at": event.created_at.isoformat(),
+    }
+
+
 @router.post("/score")
 async def get_score(req: ScoreRequest, session: AsyncSession = Depends(get_session)):
     """Compute the contextual feedback score for a track given a vibe description."""