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

plugin/server/api.go

@@ -75,6 +75,7 @@ type CreateSessionRequest struct {
 	ChannelID  string `json:"channel_id"`
 	RootID     string `json:"root_id,omitempty"`
 	AgentID    string `json:"agent_id"`
+	BotUserID  string `json:"bot_user_id,omitempty"`
 }
 
 // handleCreateSession creates a new custom_livestatus post and starts tracking.
@@ -98,8 +99,20 @@ func (p *Plugin) handleCreateSession(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	// Create the custom post
+	// Create the custom post — UserId is required
+	// Use the bot user ID passed in the request, or fall back to plugin bot
+	userID := req.BotUserID
+	if userID == "" {
+		// Try to get plugin's own bot
+		userID = p.getBotUserID()
+	}
+	if userID == "" {
+		writeJSON(w, http.StatusBadRequest, map[string]string{"error": "bot_user_id required (no plugin bot available)"})
+		return
+	}
+
 	post := &model.Post{
+		UserId:    userID,
 		ChannelId: req.ChannelID,
 		RootId:    req.RootID,
 		Type:      "custom_livestatus",