Write unit tests for LocalStorageAdapter

Keep the test file strictly focused on LocalStorageAdapter behavior — do not test OrgSelectionStorageKeys constants here (those have their own test per task-001). Use descriptive test names that read as sentences: test('returns null when key has not been written', ...) rather than test('readString null', ...). Group tests by method using group('readString', ...) blocks for readability. For the concurrent test, note that SharedPreferences mock in flutter_test is synchronous under the hood — the concurrency test primarily validates that the adapter does not introduce any accidental state mutation between calls.

If the adapter internally caches values, the concurrent test will catch stale-read bugs. Add a comment at the top of the test file referencing the 100% coverage requirement so future contributors know not to reduce coverage.

All tests are pure unit tests using flutter_test — no WidgetTester needed. Call SharedPreferences.setMockInitialValues({}) in setUp() to reset state between tests; do not rely on test execution order. For the concurrent write test, use Future.wait([adapter.writeString(key1, val1), adapter.writeString(key2, val2)]) and then read both keys to assert both persisted. For the FormatException test, use SharedPreferences.setMockInitialValues({'org_selection.bad_key': 'not-valid-json{{'}) and then call adapter.readJson('org_selection.bad_key', (m) => m) and expect it to throw FormatException.

Run coverage with: flutter test --coverage test/infrastructure/local_storage_adapter_test.dart and inspect lcov.info to confirm 100% branch coverage. If coverage is below 100%, identify the uncovered branch (likely a null-check or catch block) and add a targeted test case.