feat(seed-saving): per-crop 'how to save this seed' guidance

A bundled, curated knowledge layer — the differentiator of a serious
seed app. For a variety's crop it shows how the plant reproduces and what
it takes to keep the variety true: life cycle, pollination (self/cross +
insect/wind), isolation distance, how many plants to save from, dry/wet
processing, a difficulty pill, and a short tip — all in human words.

- assets/catalog/seed_saving.json: curated public-domain data (Seed to
  Seed / Seed Savers), keyed by botanical FAMILY (defaults) with
  per-species/genus OVERRIDES that win — so e.g. Vicia faba is correctly
  insect-cross-pollinated despite the selfing Fabaceae default, and maize
  is wind-pollinated with a large population. Notes are locale-keyed
  (es/en), extensible to any language — a starter set, not a ceiling.
- domain/seed_saving.dart (pure): enums + SeedSavingGuide (merge, note
  fallback) + SeedSavingData.guideFor (species → genus → family).
- data/seed_saving_catalog.dart: loads the asset once into an in-memory
  singleton (no DB table, no migration); injector loads it at startup.
- VarietyDetail gains  (from the linked species — the reliable
  key, vs the editable category); detail screen shows a _SeedSavingView
  when a guide resolves.
- i18n seedSaving block (labels + enum values + params) in en/es/pt/ast.
- Tests: domain lookup/merge, the real asset's key corrections, and the
  detail section shows/hides. 314 suite tests green; analyze clean.

apps/app_seeds/test/ui/seed_saving_section_test.dart

@@ -0,0 +1,54 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/data/seed_saving_catalog.dart';
+import 'package:tane/db/database.dart';
+import 'package:tane/domain/seed_saving.dart';
+
+import '../support/test_support.dart';
+
+/// The variety detail shows "how to save this seed" when the bundled catalog
+/// has guidance for the crop's family, and hides it otherwise.
+void main() {
+  late AppDatabase db;
+  setUp(() {
+    db = newTestDatabase();
+    SeedSavingCatalog.data = parseSeedSaving('''
+    {
+      "families": {
+        "Solanaceae": { "pollination": "self", "isolationMinM": 3, "isolationMaxM": 6, "processing": "wet", "difficulty": "easy" }
+      },
+      "species": {}
+    }
+    ''');
+  });
+  tearDown(() {
+    SeedSavingCatalog.data = null;
+    return db.close();
+  });
+
+  Future<void> pumpDetailFor(WidgetTester tester, String? category) async {
+    final repo = newTestRepository(db);
+    final id = await repo.addQuickVariety(label: 'Tomate', category: category);
+    await tester.pumpWidget(wrapDetail(repository: repo, varietyId: id));
+    await tester.pumpAndSettle();
+  }
+
+  testWidgets('shows the seed-saving section for a known family', (tester) async {
+    await pumpDetailFor(tester, 'Solanaceae');
+
+    expect(find.text('Saving its seed'), findsOneWidget);
+    // The pollination line is a Text.rich (label + value), so match the run.
+    expect(find.textContaining('Self-pollinating'), findsOneWidget);
+    expect(find.text('Easy'), findsOneWidget); // the difficulty pill
+
+    await disposeTree(tester);
+  });
+
+  testWidgets('hides the section when nothing matches', (tester) async {
+    await pumpDetailFor(tester, 'Unknownaceae');
+
+    expect(find.text('Saving its seed'), findsNothing);
+
+    await disposeTree(tester);
+  });
+}