Implement Duplicate Queue Repository

Model DuplicateQueueStatus as a Dart enum with a `fromString` factory that throws on unknown values — never use raw strings from the database as enum values without validation. The DuplicateQueuePage value object should carry both `items` and `totalCount` so the UI can render a progress indicator (e.g., '12 of 47 resolved'). For the coordinator queue, NHF's structure of 12 landsforeninger × 9 regioner × 1,400 chapters means a coordinator's scope may span multiple chapters — the `coordinator_scope` should be stored as a list of chapter IDs, not a single FK. Pitfall: offset-based pagination becomes inconsistent if items are inserted between page fetches (coordinator sees duplicates or gaps).

Consider cursor-based pagination using `created_at + id` composite cursor for production stability. If Supabase Realtime is scoped into this task, use `supabase.channel()` with a filter on `coordinator_id` to avoid broadcasting all queue changes to all clients.

Unit tests using flutter_test with mocked Supabase client. Test scenarios: (1) first page returned with correct count and hasNextPage=true; (2) last page returns hasNextPage=false; (3) status filter returns only matching items; (4) valid status transition succeeds; (5) invalid transition (e.g., resolved→pending) throws DuplicateQueueTransitionException; (6) enqueue creates item in pending status with correct coordinator assignment; (7) RLS violation (coordinator accessing another chapter's queue) surfaces as typed PermissionException. Integration tests against local Supabase: seed 25 queue items across 3 coordinators, verify pagination returns correct subsets per coordinator. Test that Supabase Realtime subscription (if implemented) delivers a new item event within 2 seconds of insertion.