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/file-io.ts

@@ -397,6 +397,34 @@ export async function readDecisionFiles(agentWorkdir: string): Promise<ParsedDec
   });
 }
 
+export interface ParsedCommentResponse {
+  commentId: string;
+  body: string;
+  resolved?: boolean;
+}
+
+export async function readCommentResponses(agentWorkdir: string): Promise<ParsedCommentResponse[]> {
+  const filePath = join(agentWorkdir, '.cw', 'output', 'comment-responses.json');
+  try {
+    const raw = await readFile(filePath, 'utf-8');
+    const parsed = JSON.parse(raw);
+    if (!Array.isArray(parsed)) return [];
+    return parsed
+      .filter((entry: unknown) => {
+        if (typeof entry !== 'object' || entry === null) return false;
+        const e = entry as Record<string, unknown>;
+        return typeof e.commentId === 'string' && typeof e.body === 'string';
+      })
+      .map((entry: Record<string, unknown>) => ({
+        commentId: String(entry.commentId),
+        body: String(entry.body),
+        resolved: typeof entry.resolved === 'boolean' ? entry.resolved : undefined,
+      }));
+  } catch {
+    return [];
+  }
+}
+
 export async function readPageFiles(agentWorkdir: string): Promise<ParsedPageFile[]> {
   const dirPath = join(agentWorkdir, '.cw', 'output', 'pages');
   return readFrontmatterDir(dirPath, (data, body, filename) => {