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

web/src/app/infra/http/BackendClient.ts

@@ -1007,4 +1007,50 @@ export class BackendClient extends BaseHttpClient {
 
     return this.get(`/api/v1/monitoring/overview?${queryParams.toString()}`);
   }
+
+  // ============ Survey API ============
+  public getSurveyPending(): Promise<{
+    survey: {
+      survey_id: string;
+      version: number;
+      title: Record<string, string>;
+      description: Record<string, string>;
+      questions: SurveyQuestion[];
+    } | null;
+  }> {
+    return this.get('/api/v1/survey/pending');
+  }
+
+  public submitSurveyResponse(
+    surveyId: string,
+    answers: Record<string, unknown>,
+    completed: boolean = true,
+  ): Promise<object> {
+    return this.post('/api/v1/survey/respond', {
+      survey_id: surveyId,
+      answers,
+      completed,
+    });
+  }
+
+  public dismissSurvey(surveyId: string): Promise<object> {
+    return this.post('/api/v1/survey/dismiss', { survey_id: surveyId });
+  }
+}
+
+export interface SurveyQuestion {
+  id: string;
+  type: 'single_select' | 'multi_select' | 'text';
+  title: Record<string, string>;
+  subtitle?: Record<string, string>;
+  required: boolean;
+  options?: SurveyOption[];
+  placeholder?: Record<string, string>;
+  max_length?: number;
+}
+
+export interface SurveyOption {
+  id: string;
+  label: Record<string, string>;
+  has_input?: boolean;
 }