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/ui/variety_detail_screen.dart

@@ -139,6 +139,20 @@ class _DetailView extends StatelessWidget {
                 subtitle: lot.storageLocation == null
                     ? null
                     : Text(lot.storageLocation!),
+                trailing: Row(
+                  mainAxisSize: MainAxisSize.min,
+                  children: [
+                    if (lot.latestGerminationRate != null)
+                      _GerminationBadge(rate: lot.latestGerminationRate!),
+                    IconButton(
+                      key: Key('lot.germination.${lot.id}'),
+                      icon: const Icon(Icons.grass_outlined),
+                      tooltip: t.germination.title,
+                      onPressed: () =>
+                          _showGerminationSheet(context, cubit, lot),
+                    ),
+                  ],
+                ),
               ),
         ],
       ),
@@ -166,6 +180,135 @@ String _quantityLabel(Translations t, Quantity q) {
 String _trimDouble(double v) =>
     v == v.roundToDouble() ? v.toStringAsFixed(0) : v.toString();
 
+String _germinationPercent(Translations t, double rate) =>
+    t.germination.result(percent: (rate * 100).round());
+
+/// A compact pill showing the latest germination rate on a lot tile.
+class _GerminationBadge extends StatelessWidget {
+  const _GerminationBadge({required this.rate});
+
+  final double rate;
+
+  @override
+  Widget build(BuildContext context) {
+    final scheme = Theme.of(context).colorScheme;
+    return Container(
+      padding: const EdgeInsets.symmetric(horizontal: 8, vertical: 4),
+      decoration: BoxDecoration(
+        color: scheme.secondaryContainer,
+        borderRadius: BorderRadius.circular(12),
+      ),
+      child: Text(
+        _germinationPercent(context.t, rate),
+        style: TextStyle(
+          color: scheme.onSecondaryContainer,
+          fontWeight: FontWeight.w600,
+        ),
+      ),
+    );
+  }
+}
+
+Future<void> _showGerminationSheet(
+  BuildContext context,
+  VarietyDetailCubit cubit,
+  VarietyLot lot,
+) {
+  final t = context.t;
+  final sample = TextEditingController();
+  final germinated = TextEditingController();
+  return showModalBottomSheet<void>(
+    context: context,
+    isScrollControlled: true,
+    builder: (sheetContext) => Padding(
+      padding: EdgeInsets.only(
+        left: 16,
+        right: 16,
+        top: 16,
+        bottom: MediaQuery.of(sheetContext).viewInsets.bottom + 16,
+      ),
+      child: Column(
+        mainAxisSize: MainAxisSize.min,
+        crossAxisAlignment: CrossAxisAlignment.stretch,
+        children: [
+          Text(
+            t.germination.title,
+            style: Theme.of(sheetContext).textTheme.titleLarge,
+          ),
+          const SizedBox(height: 8),
+          if (lot.germinationTests.isEmpty)
+            Text(t.germination.none)
+          else
+            for (final test in lot.germinationTests)
+              ListTile(
+                dense: true,
+                contentPadding: EdgeInsets.zero,
+                leading: const Icon(Icons.grass_outlined),
+                title: Text(
+                  test.rate == null ? '—' : _germinationPercent(t, test.rate!),
+                ),
+                subtitle:
+                    (test.sampleSize != null && test.germinatedCount != null)
+                    ? Text('${test.germinatedCount}/${test.sampleSize}')
+                    : null,
+              ),
+          const Divider(),
+          Row(
+            children: [
+              Expanded(
+                child: TextField(
+                  key: const Key('germination.germinated'),
+                  controller: germinated,
+                  keyboardType: TextInputType.number,
+                  decoration: InputDecoration(
+                    labelText: t.germination.germinated,
+                    border: const OutlineInputBorder(),
+                  ),
+                ),
+              ),
+              const SizedBox(width: 12),
+              Expanded(
+                child: TextField(
+                  key: const Key('germination.sampleSize'),
+                  controller: sample,
+                  keyboardType: TextInputType.number,
+                  decoration: InputDecoration(
+                    labelText: t.germination.sampleSize,
+                    border: const OutlineInputBorder(),
+                  ),
+                ),
+              ),
+            ],
+          ),
+          const SizedBox(height: 16),
+          Row(
+            children: [
+              TextButton(
+                onPressed: () => Navigator.of(sheetContext).pop(),
+                child: Text(t.common.cancel),
+              ),
+              const Spacer(),
+              FilledButton(
+                key: const Key('germination.save'),
+                onPressed: () {
+                  cubit.addGerminationTest(
+                    lotId: lot.id,
+                    testedOn: DateTime.now().millisecondsSinceEpoch,
+                    sampleSize: int.tryParse(sample.text.trim()),
+                    germinatedCount: int.tryParse(germinated.text.trim()),
+                  );
+                  Navigator.of(sheetContext).pop();
+                },
+                child: Text(t.germination.add),
+              ),
+            ],
+          ),
+        ],
+      ),
+    ),
+  );
+}
+
 Future<void> _confirmDelete(
   BuildContext context,
   VarietyDetailCubit cubit,