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

apps/server/agent/output-handler.ts

@@ -15,6 +15,7 @@ import type { PhaseRepository } from '../db/repositories/phase-repository.js';
 import type { TaskRepository } from '../db/repositories/task-repository.js';
 import type { PageRepository } from '../db/repositories/page-repository.js';
 import type { ChatSessionRepository } from '../db/repositories/chat-session-repository.js';
+import type { ReviewCommentRepository } from '../db/repositories/review-comment-repository.js';
 import type {
   EventBus,
   AgentStoppedEvent,
@@ -37,6 +38,7 @@ import {
   readDecisionFiles,
   readPageFiles,
   readFrontmatterFile,
+  readCommentResponses,
 } from './file-io.js';
 import { getProvider } from './providers/registry.js';
 import { markdownToTiptapJson } from './markdown-to-tiptap.js';
@@ -92,6 +94,7 @@ export class OutputHandler {
     private pageRepository?: PageRepository,
     private signalManager?: SignalManager,
     private chatSessionRepository?: ChatSessionRepository,
+    private reviewCommentRepository?: ReviewCommentRepository,
   ) {}
 
   /**
@@ -851,6 +854,28 @@ export class OutputHandler {
       }
     }
 
+    // Process comment responses from agent (for review/execute tasks)
+    if (this.reviewCommentRepository) {
+      try {
+        const commentResponses = await readCommentResponses(agentWorkdir);
+        for (const resp of commentResponses) {
+          try {
+            await this.reviewCommentRepository.createReply(resp.commentId, resp.body, 'agent');
+            if (resp.resolved) {
+              await this.reviewCommentRepository.resolve(resp.commentId);
+            }
+          } catch (err) {
+            log.warn({ agentId, commentId: resp.commentId, err: err instanceof Error ? err.message : String(err) }, 'failed to process comment response');
+          }
+        }
+        if (commentResponses.length > 0) {
+          log.info({ agentId, count: commentResponses.length }, 'processed agent comment responses');
+        }
+      } catch (err) {
+        log.warn({ agentId, err: err instanceof Error ? err.message : String(err) }, 'failed to read comment responses');
+      }
+    }
+
     const resultPayload: AgentResult = {
       success: true,
       message: resultMessage,