fix: plugin bot user + await plugin detection before session scan

- Add EnsureBotUser on plugin activate (fixes 'Unable to find user' error)
- Accept bot_user_id in create session request
- Await plugin health check before starting session monitor
  (prevents race where sessions detect before plugin flag is set)
- Plugin now creates custom_livestatus posts with proper bot user

src/watcher-manager.js

@@ -171,13 +171,17 @@ async function startDaemon() {
       logger: logger.child({ module: 'plugin-client' }),
     });
 
-    // Initial plugin detection
-    pluginClient.isHealthy().then(function (healthy) {
+    // Initial plugin detection (awaited before monitor starts — see below)
+    try {
+      var healthy = await pluginClient.isHealthy();
       usePlugin = healthy;
       logger.info({ usePlugin, url: config.plugin.url }, healthy
         ? 'Plugin detected — using WebSocket rendering mode'
         : 'Plugin not available — using REST API fallback');
-    });
+    } catch (_detectErr) {
+      usePlugin = false;
+      logger.warn('Plugin detection failed — using REST API fallback');
+    }
 
     // Periodic re-detection
     setInterval(function () {