# Task: Migrate POST/PUT/DELETE endpoints to AlertService

## Goal
Replace `routers/alerts.py` write endpoints (`create_alert`, `update_alert`, `resolve_alert`, `dismiss_alert`) to use `AlertService`.

## Requirements

### Changes to `src/backend/routers/alerts.py`

1. Replace `create_alert()` body:
   - Call `service.create_alert(watchlist_id, type, trigger_type, message, severity, ticker, metadata, user_id)`
   - Return `AlertResponse` wrapping the result
   - Keep the watchlist owner check

2. Replace `update_alert()` body:
   - Use `service.get_alert()` to verify existence and ownership
   - Build updates dict from `body` fields
   - Call `service.update_alert(alert_id, updates_dict, user_id)`
   - Return `AlertResponse` wrapping the result

3. Replace `resolve_alert()` body:
   - Use `service.get_alert()` to verify existence and ownership
   - Call `service.resolve_alert(alert_id, user_id)`
   - Return `AlertResponse` wrapping the result

4. Replace `dismiss_alert()` body:
   - Use `service.get_alert()` to verify existence and ownership
   - Call `service.dismiss_alert(alert_id, user_id)`
   - Return `None` (204 response)

### Constraints
- Keep all route signatures, decorators, and response models unchanged
- Keep `check_all_alerts` endpoint unchanged (it calls `check_sentiment_alerts` directly)
- File must stay under 200 lines total

## Acceptance Criteria
1. All write endpoints use `AlertService` methods
2. All alert CRUD tests pass: `pytest tests/test_alerts.py -k "test_create or test_update or test_delete or test_resolve or test_dismiss" --tb=short`
3. No import errors

## Files to Modify
- `src/backend/routers/alerts.py`

## Files to Read First
- `src/backend/services/alert_service.py`
- `src/backend/routers/alerts.py` — current write endpoint implementations