feat: RHS panel initial fetch, floating widget, session cleanup (#5)

Phase 1: Fix RHS panel to fetch existing sessions on mount
- Add initial API fetch in useAllStatusUpdates() hook
- Allow GET /sessions endpoint without shared secret auth
- RHS panel now shows sessions after page refresh

Phase 2: Floating widget component (registerRootComponent)
- New floating_widget.tsx with auto-show/hide behavior
- Draggable, collapsible to pulsing dot with session count
- Shows last 5 lines of most recent active session
- Position persisted to localStorage
- CSS styles using Mattermost theme variables

Phase 3: Session cleanup and KV optimization
- Add LastUpdateMs field to SessionData for staleness tracking
- Set LastUpdateMs on session create and update
- Add periodic cleanup goroutine (every 5 min)
- Stale active sessions (>30 min no update) marked interrupted
- Expired non-active sessions (>1 hr) deleted from KV
- Add ListAllSessions and keep ListActiveSessions as helper
- Add debug logging to daemon file polling

Closes #5

src/status-watcher.js

@@ -107,16 +107,27 @@ class StatusWatcher extends EventEmitter {
   _startFilePoll(sessionKey, state) {
     var self = this;
     var pollInterval = 500; // 500ms poll
+    var pollCount = 0;
     state._filePollTimer = setInterval(function () {
       try {
         var stat = fs.statSync(state.transcriptFile);
+        pollCount++;
         if (stat.size > state.lastOffset) {
+          if (self.logger) {
+            self.logger.info(
+              { sessionKey, fileSize: stat.size, lastOffset: state.lastOffset, delta: stat.size - state.lastOffset, pollCount },
+              'File poll: new data detected — reading',
+            );
+          }
           self._readFile(sessionKey, state);
         }
       } catch (_e) {
         // File might not exist yet or was deleted
       }
     }, pollInterval);
+    if (self.logger) {
+      self.logger.info({ sessionKey, pollInterval }, 'File poll timer started');
+    }
   }
 
   /**
@@ -214,6 +225,9 @@ class StatusWatcher extends EventEmitter {
     const state = this.sessions.get(sessionKey);
     if (!state) return;
 
+    if (this.logger) {
+      this.logger.info({ sessionKey, fullPath: path.basename(fullPath) }, 'fs.watch: file change detected');
+    }
     this._readFile(sessionKey, state);
   }