Unit test ReportHistoryRepository with mock Supabase client

Supabase Flutter's query builder uses a fluent API that returns the same builder object from filter methods, making it chainable. To mock this correctly, each chained method (`.from()`, `.select()`, `.eq()`, `.range()`, `.order()`) must return the mock builder itself: `when(mockBuilder.eq(any, any)).thenReturn(mockBuilder)`. The final terminal call (`.execute()` or awaited result) returns the `PostgrestResponse`. If the repository uses the newer `supabase_flutter` API where `.select()` directly returns a `Future>`, adjust mocking accordingly — check the exact version used in `pubspec.yaml`.

Organize test file as `report_history_repository_test.dart`. Use `const` fixture maps for expected JSON payloads to keep assertions readable. Add a dedicated test group `'organization_id scoping'` that runs the same check across all public methods to make the security invariant explicit.

Pure unit tests using Mockito mocks. Use `@GenerateMocks([SupabaseClient, SupabaseQueryBuilder, PostgrestFilterBuilder])` annotations and run `flutter pub run build_runner build` to generate `.mocks.dart` files. Structure: one `group()` per repository method, with sub-cases for success and each error scenario. Use `when(mockClient.from('bufdir_report_history')).thenReturn(mockQueryBuilder)` to chain mock responses.

Assert both the return value (correct deserialization) and the call arguments (correct query construction). Verify `organization_id` filter presence using `verify(mockBuilder.eq('organization_id', any)).called(greaterThanOrEqualTo(1))`. Test error mapping by having the mock throw `PostgrestException` and asserting the repository re-throws the correct domain exception type.