feat: Add threaded review comments + agent comment responses

Introduces GitHub-style threaded comments via parentCommentId self-reference.
Users and agents can reply within comment threads, and review agents receive
comment IDs so they can post targeted responses via comment-responses.json.

- Migration 0032: parentCommentId column + index on review_comments
- Repository: createReply() copies parent context, default author 'you' → 'user'
- tRPC: replyToReviewComment procedure, requestPhaseChanges passes threaded comments
- Orchestrator: formats [comment:ID] tags with full reply threads in task description
- Agent IO: readCommentResponses() reads .cw/output/comment-responses.json
- OutputHandler: processes agent comment responses (creates replies, resolves threads)
- Execute prompt: conditional <review_comments> block when task has [comment:] markers
- Frontend: CommentThread renders root+replies with agent-specific styling + reply form
- Sidebar/ReviewTab: root-only comment counts, reply mutation plumbing through DiffViewer chain

docs/dispatch-events.md

@@ -123,5 +123,5 @@ Multiple rapid events (e.g. several `phase:queued` from `queueAllPhases`) are co
 
 - **YOLO**: phase completes → auto-merge → auto-dispatch next phase → auto-dispatch tasks
 - **review_per_phase**: phase completes → set `pending_review` → STOP. User approves → `approveAndMergePhase()` → merge → dispatch next phase → dispatch tasks
-- **request-changes (phase)**: phase `pending_review` → user requests changes → creates revision task (category=`'review'`, dedup guard skips if active review exists) → phase reset to `in_progress` → agent fixes → phase returns to `pending_review`
+- **request-changes (phase)**: phase `pending_review` → user requests changes → creates revision task (category=`'review'`, dedup guard skips if active review exists) with threaded comments (`[comment:ID]` tags + reply threads) → phase reset to `in_progress` → agent reads comments, fixes code, writes `.cw/output/comment-responses.json` → OutputHandler creates reply comments and optionally resolves threads → phase returns to `pending_review`
 - **request-changes (initiative)**: initiative `pending_review` → user requests changes → creates/reuses "Finalization" phase → creates review task → initiative reset to `active` → agent fixes → initiative returns to `pending_review`