Implement FCM push notification dispatch for pause events

Create a Supabase Edge Function named 'dispatch-pause-notification' that accepts a JSON body with { event_type, mentor_id, mentor_name, coordinator_id, organisation_id }. The function should: (1) validate the caller's JWT org claim matches organisation_id, (2) query device_tokens for active tokens for coordinator_id, (3) build FCM messages using the HTTP v1 API format with the service account JWT (obtained via Google's OAuth2 token endpoint using the service account key), (4) dispatch all tokens in parallel using Promise.all, (5) process results and deactivate invalid tokens. In the Flutter PauseNotificationService, invoke the Edge Function using Supabase's functions.invoke() method — this automatically attaches the user's JWT. For deep link routing on notification tap, use the flutter_local_notifications or firebase_messaging onMessageOpenedApp handler to parse the data.deep_link field and push the appropriate named route.

Ensure the retry logic in the Edge Function uses Deno's built-in setTimeout wrapped in a Promise — do not use a blocking sleep.

Write unit tests for the Supabase Edge Function covering: (1) correct FCM payload structure built for pause_activated event, (2) correct payload for mentor_reactivated event, (3) invalid/not-found FCM token triggers device_tokens deactivation, (4) rate-limit 429 triggers one retry with delay, (5) second retry failure logs error without throwing, (6) JWT with wrong organisation claim is rejected before token resolution. Write a Flutter unit test for PauseNotificationService asserting: (7) Edge Function is invoked with the correct coordinator_id and event type after pause/reactivation. Test the no-tokens case asserting the function returns without error. Use a mock FCM endpoint in tests — do not call the real FCM API.