feat(persistence): add user feedback + follow-up run association

Phase 2-C: feedback and follow-up tracking.

- FeedbackRow ORM model (rating +1/-1, optional message_id, comment)
- FeedbackRepository with CRUD, list_by_run/thread, aggregate stats
- Feedback API endpoints: create, list, stats, delete
- follow_up_to_run_id in RunCreateRequest (explicit or auto-detected
  from latest successful run on the thread)
- Worker writes follow_up_to_run_id into human_message event metadata
- Gateway deps: feedback_repo factory + getter
- 17 new tests (14 FeedbackRepository + 3 follow-up association)
- 109 total tests pass, zero regressions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/packages/harness/deerflow/persistence/models/__init__.py

@@ -1,5 +1,6 @@
+from deerflow.persistence.models.feedback import FeedbackRow
 from deerflow.persistence.models.run import RunRow
 from deerflow.persistence.models.run_event import RunEventRow
 from deerflow.persistence.models.thread_meta import ThreadMetaRow
 
-__all__ = ["RunEventRow", "RunRow", "ThreadMetaRow"]
+__all__ = ["FeedbackRow", "RunEventRow", "RunRow", "ThreadMetaRow"]

backend/packages/harness/deerflow/persistence/models/feedback.py

@@ -0,0 +1,30 @@
+"""ORM model for user feedback on runs."""
+
+from __future__ import annotations
+
+from datetime import UTC, datetime
+
+from sqlalchemy import String, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from deerflow.persistence.base import Base
+
+
+class FeedbackRow(Base):
+    __tablename__ = "feedback"
+
+    feedback_id: Mapped[str] = mapped_column(String(64), primary_key=True)
+    run_id: Mapped[str] = mapped_column(String(64), nullable=False, index=True)
+    thread_id: Mapped[str] = mapped_column(String(64), nullable=False, index=True)
+    owner_id: Mapped[str | None] = mapped_column(String(64), index=True)
+    message_id: Mapped[str | None] = mapped_column(String(64))
+    # message_id is an optional RunEventStore event identifier —
+    # allows feedback to target a specific message or the entire run
+
+    rating: Mapped[int] = mapped_column(nullable=False)
+    # +1 (thumbs-up) or -1 (thumbs-down)
+
+    comment: Mapped[str | None] = mapped_column(Text)
+    # Optional text feedback from the user
+
+    created_at: Mapped[datetime] = mapped_column(default=lambda: datetime.now(UTC))