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)

src/watcher-manager.js

@@ -240,14 +240,6 @@ async function startDaemon() {
         const initialText = buildInitialText(agentId, sessionKey);
         postId = await sharedStatusBox.createPost(channelId, initialText, rootPostId);
         logger.info({ sessionKey, postId, channelId }, 'Created status box');
-
-        // Auto-pin the status post so it's always visible
-        try {
-          await sharedStatusBox._apiCall('POST', '/api/v4/posts/' + postId + '/pin', {});
-          logger.debug({ sessionKey, postId }, 'Status post pinned');
-        } catch (pinErr) {
-          logger.warn({ sessionKey, err: pinErr }, 'Failed to pin status post');
-        }
       } catch (err) {
         logger.error({ sessionKey, err }, 'Failed to create status post');
         globalMetrics.lastError = err.message;
@@ -339,14 +331,6 @@ async function startDaemon() {
       logger.error({ sessionKey, err }, 'Failed to update final status');
     }
 
-    // Unpin the status post when session is done
-    try {
-      await sharedStatusBox._apiCall('POST', `/api/v4/posts/${box.postId}/unpin`, {});
-      logger.debug({ sessionKey, postId: box.postId }, 'Status post unpinned');
-    } catch (unpinErr) {
-      logger.warn({ sessionKey, err: unpinErr }, 'Failed to unpin status post');
-    }
-
     // Clean up — remove from all tracking so session can be re-detected if it becomes active again
     activeBoxes.delete(sessionKey);
     watcher.removeSession(sessionKey);