feat(block1): germination tests per lot with derived rate

Record germination tests on a lot and surface the result.

- GerminationEntry model with a derived rate (germinated / sample). VarietyLot
  carries its tests (most-recent first) and exposes latestGerminationRate.
- VarietyRepository.addGerminationTest; watchVariety now also re-emits on
  germination-test changes, so the detail refreshes live.
- Detail UI: each lot shows a germination % badge and a grass action that opens
  a sheet listing past tests and adding a new one (germinated + sample size).
  i18n strings (ES/EN).

Tests: derived-rate + reactivity at the repository, and a widget test for the
record-test → badge flow. Full suite: 35 passing, 0 skipped.

apps/app_seeds/lib/state/variety_detail_cubit.dart

@@ -56,6 +56,18 @@ class VarietyDetailCubit extends Cubit<VarietyDetailState> {
   Future<void> linkSpecies(String speciesId) =>
       _repo.linkSpecies(varietyId, speciesId);
 
+  Future<void> addGerminationTest({
+    required String lotId,
+    int? testedOn,
+    int? sampleSize,
+    int? germinatedCount,
+  }) => _repo.addGerminationTest(
+    lotId: lotId,
+    testedOn: testedOn,
+    sampleSize: sampleSize,
+    germinatedCount: germinatedCount,
+  );
+
   Future<void> deleteVariety() async {
     await _repo.softDeleteVariety(varietyId);
     emit(