feat: beta feedback widget — frictionless in-session feedback

Full-stack beta feedback system:

Backend:
- BetaFeedback model with reaction, category, text, page context
- POST /feedback/beta (any auth user), GET /feedback/beta (admin, filtered)
- Alembic migration 065 with indexes on user_id, reaction, created_at

Frontend:
- Persistent "Feedback" tab on right edge of all authenticated pages
- Slide-out panel: quick reaction (👍😐👎), category pills, optional text
- Auto-captures page URL and FlowPilot session ID
- Hidden on mobile (<640px), closes on Escape/outside click
- Shows "Thanks!" confirmation then auto-closes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/api/betaFeedback.ts

@@ -0,0 +1,6 @@
+import { apiClient } from './client'
+
+export const betaFeedbackApi = {
+  submit: (data: { reaction: string; category?: string; text?: string; page_url?: string; session_id?: string }) =>
+    apiClient.post('/feedback/beta', data).then(r => r.data),
+}

frontend/src/api/index.ts

@@ -31,3 +31,4 @@ export { notificationsApi } from './notifications'
 export { publicTemplatesApi } from './publicTemplates'
 export { uploadsApi, default as uploadsApiDefault } from './uploads'
 export { scriptBuilderApi } from './scriptBuilder'
+export { betaFeedbackApi } from './betaFeedback'