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)

hooks/status-watcher-hook/HOOK.md

@@ -1,7 +1,7 @@
 ---
 name: status-watcher-hook
-description: "Auto-starts the Live Status v4 watcher daemon on gateway startup"
-metadata: { "openclaw": { "emoji": "📡", "events": ["gateway:startup"] } }
+description: 'Auto-starts the Live Status v4 watcher daemon on gateway startup'
+metadata: { 'openclaw': { 'emoji': '📡', 'events': ['gateway:startup'] } }
 ---
 
 # status-watcher-hook