The frontend test notification feature was calling /api/test-notifications/trigger,
but this endpoint didn't exist in the backend, causing a 404 HTML response that
failed JSON parsing with the error "JSON.parse: unexpected character at line 1 column 1".
Changes:
- Added triggerTestNotification service method to handle test notification creation
- Added triggerTestNotification controller method to handle the API request
- Registered POST /test-notifications/trigger route
- Implemented type mapping for all notification types (task_due_soon, task_overdue,
defer_until, project_due_soon, project_overdue)
- Test notifications respect user notification preferences and send to enabled channels
- Returns notification details with sources (in-app, telegram) sent to
Fixes#1002
