feat: Session persistence with Redis + Draft management fixes

- Implement session management API (/api/v1/session/create, verify, logout)
- Add session restoration from localStorage on page reload
- Fix session_id priority when loading drafts (use current, not old from DB)
- Add unified_id and claim_id to wizard payload sent to n8n
- Add Docker volume for frontend HMR (Hot Module Replacement)
- Add comprehensive session logging for debugging

Components updated:
- backend/app/api/session.py (NEW) - Session management endpoints
- backend/app/main.py - Include session router
- frontend/src/components/form/Step1Phone.tsx v2.0 - Create session after SMS
- frontend/src/pages/ClaimForm.tsx v3.8 - Session restoration & priority fix
- frontend/src/components/form/StepWizardPlan.tsx v1.4 - Add unified_id/claim_id
- docker-compose.yml - Add frontend volume for live reload

Session flow:
1. User verifies phone -> session created in Redis (24h TTL)
2. session_token saved to localStorage
3. Page reload -> session restored automatically
4. Draft selected -> current session_id used (not old from DB)
5. Wizard submit -> unified_id, claim_id, session_id sent to n8n
6. Logout -> session removed from Redis & localStorage

Fixes:
- Session token not persisting after page reload
- unified_id missing in n8n webhook payload
- Old session_id from draft overwriting current session
- Frontend changes requiring container rebuild

frontend/src/components/form/Step2Details.tsx

@@ -302,7 +302,7 @@ export default function Step2Details({ formData, updateFormData, onNext, onPrev,
       uploadFormData.append('file_type', currentDocConfig.file_type);
       uploadFormData.append('filename', currentFile.name);
       uploadFormData.append('voucher', formData.voucher || '');
-      uploadFormData.append('session_id', sessionStorage.getItem('session_id') || 'unknown');
+      uploadFormData.append('session_id', formData.session_id || 'unknown');
       uploadFormData.append('upload_timestamp', new Date().toISOString());
       uploadFormData.append('file', currentFile);