feat: add in-product survey system (#2008)

* feat: add in-product survey system

- SurveyManager: event-based trigger, Space API communication
- Trigger on first successful non-WebSocket response
- Backend API: /api/v1/survey/{pending,respond,dismiss}
- Frontend: floating survey widget with progressive questions
- Flat radio/checkbox style (not dropdown Select)

* fix: persist triggered survey events to disk across restarts

Store triggered events in data/survey_triggered_events.json so that
restarting the process doesn't re-query Space for already-triggered events.

* fix: use metadata table for survey event persistence instead of file

Store triggered events in the existing metadata KV table
(key='survey_triggered_events') instead of a standalone JSON file.

* fix: ruff format and prettier fixes

src/langbot/pkg/pipeline/process/handlers/chat.py

@@ -200,6 +200,11 @@ class ChatMessageHandler(handler.MessageHandler):
 
                     # Send telemetry asynchronously and do not block pipeline via app's telemetry manager
                     await self.ap.telemetry.start_send_task(payload)
+
+                    # Trigger survey event on first successful non-WebSocket response
+                    if not locals().get('error_info') and adapter_name and 'WebSocket' not in adapter_name:
+                        if self.ap.survey:
+                            await self.ap.survey.trigger_event('first_bot_response_success')
                 except Exception as ex:
                     # Ensure telemetry issues do not affect normal flow
                     self.ap.logger.warning(f'Failed to send telemetry: {ex}')