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/data/seed_saving_asset_test.dart

@@ -0,0 +1,51 @@
+import 'dart:io';
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:tane/domain/seed_saving.dart';
+
+/// Guards the committed bundled seed-saving asset: it must parse, cover the
+/// major families, and carry the notable per-species corrections the UI relies
+/// on. Reads the file directly — no Flutter asset bundle — so it runs as a
+/// plain VM test.
+void main() {
+  final data =
+      parseSeedSaving(File('assets/catalog/seed_saving.json').readAsStringSync());
+
+  test('resolves the major families', () {
+    for (final family in const [
+      'Solanaceae',
+      'Fabaceae',
+      'Cucurbitaceae',
+      'Brassicaceae',
+      'Asteraceae',
+      'Apiaceae',
+      'Amaranthaceae',
+      'Poaceae',
+    ]) {
+      expect(data.guideFor(family: family)?.hasAny, isTrue, reason: family);
+    }
+  });
+
+  test('faba bean is corrected to insect cross-pollination', () {
+    // The whole point of species overrides: unlike other legumes, Vicia faba
+    // crosses — the guidance must not inherit Fabaceae "self".
+    final g = data.guideFor(scientificName: 'Vicia faba', family: 'Fabaceae');
+    expect(g?.pollination, Pollination.cross);
+    expect(g?.vector, PollinationVector.insect);
+    expect(g?.noteFor('es'), isNotNull);
+  });
+
+  test('tomato self-pollinates and is wet-processed', () {
+    final g = data.guideFor(
+        scientificName: 'Solanum lycopersicum', family: 'Solanaceae');
+    expect(g?.pollination, Pollination.self);
+    expect(g?.processing, SeedProcessing.wet);
+    expect(g?.difficulty, SavingDifficulty.easy);
+  });
+
+  test('maize is wind-pollinated with a large population', () {
+    final g = data.guideFor(scientificName: 'Zea mays', family: 'Poaceae');
+    expect(g?.vector, PollinationVector.wind);
+    expect(g?.recommendedPlants, greaterThanOrEqualTo(50));
+  });
+}