fix: remove dead delete+recreate and pin code, add poll fallback test

Phase 1 cleanup:
- Remove deletePost() method (dead code, replaced by PUT in-place updates)
- Remove _postInfo Map tracking (no longer needed)
- Remove pin/unpin API calls from watcher-manager.js (incompatible with PUT updates)
- Add JSDoc note on (edited) label limitation in _flushUpdate()
- Add integration test: test/integration/poll-fallback.test.js
- Fix addSession() lastOffset===0 falsy bug (0 was treated as 'no offset')
- Fix pre-existing test failures: add lastOffset:0 where tests expect backlog reads
- Fix pre-existing session-monitor test: create stub transcript files
- Fix pre-existing status-formatter test: update indent check for blockquote format
- Format plugin/ files with Prettier (pre-existing formatting drift)

test/integration/session-monitor.test.js

@@ -21,6 +21,17 @@ function writeSessionsJson(dir, agentId, sessions) {
   const agentDir = path.join(dir, agentId, 'sessions');
   fs.mkdirSync(agentDir, { recursive: true });
   fs.writeFileSync(path.join(agentDir, 'sessions.json'), JSON.stringify(sessions, null, 2));
+  // Create stub transcript files so SessionMonitor's stale-check doesn't skip them
+  for (const key of Object.keys(sessions)) {
+    const entry = sessions[key]; // eslint-disable-line security/detect-object-injection
+    const sessionId = entry.sessionId || entry.uuid;
+    if (sessionId) {
+      const transcriptPath = path.join(agentDir, `${sessionId}.jsonl`);
+      if (!fs.existsSync(transcriptPath)) {
+        fs.writeFileSync(transcriptPath, '');
+      }
+    }
+  }
 }
 
 function sleep(ms) {