Integration tests: repository and RPC bulk insert

Set up a supabase/seed.sql script under test/supabase/ that creates the minimum schema and roles needed for these tests — run it via supabase db reset before the suite. For the RLS test, create a helper createTestJwt(role: UserRole) that mints a valid JWT signed with the local JWT secret; inject it into a fresh SupabaseClient instance. For the bulk rollback test, craft a BulkRegistrationRequest where one BulkParticipant has a peer_mentor_id that violates a foreign key constraint — verify via a SELECT that the table is empty after the failed RPC call. Keep all Supabase credentials in a test/.env.test file loaded via dotenv in the test bootstrap, and add test/.env.test to .gitignore.

Structure tests so they can run in parallel (each suite inserts/deletes its own uniquely-prefixed rows) to keep total integration test time low.

Integration tests using flutter_test with real Supabase connections to a local Docker-based Supabase instance. Each test group should have a setUpAll that seeds prerequisite data (coordinator user, peer mentor user, organisation) and a tearDownAll that deletes all rows inserted during the suite. Use separate Supabase clients with different JWT roles for RLS tests — create JWTs via the test helper using the local anon and service keys. For the SharedPreferences hydration test, use shared_preferences_platform_interface's InMemorySharedPreferencesStore to avoid filesystem side effects.

Tag all tests with @Tags(['integration']) and document the required environment variables in a comment at the top of each test file.