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/unit/status-formatter.test.js

@@ -108,9 +108,10 @@ describe('status-formatter.js', () => {
       const result = format(parent);
       assert.ok(result.includes('proj035-planner'));
       assert.ok(result.includes('Reading protocol...'));
-      // Child should be indented
+      // Child should be indented — top-level uses blockquote prefix ("> ") so child
+      // lines appear as ">   ..." ("> " + depth*2 spaces). Verify indentation exists.
       const childLine = result.split('\n').find((l) => l.includes('proj035-planner'));
-      assert.ok(childLine && childLine.startsWith('  '));
+      assert.ok(childLine && /^> {2}/.test(childLine));
     });
 
     it('active session has no done footer', () => {