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/lib/data/variety_repository.dart

@@ -436,6 +436,7 @@ class VarietyDetail extends Equatable {
     this.notes,
     this.speciesId,
     this.scientificName,
+    this.family,
     this.gbifKey,
     this.wikidataQid,
     this.viabilityYears,
@@ -459,6 +460,11 @@ class VarietyDetail extends Equatable {
   final String? speciesId;
   final String? scientificName;
 
+  /// Botanical family of the linked species (Latin), the reliable key for
+  /// seed-saving guidance; null when no species is linked. (The editable
+  /// [category] is prefilled from this but may be changed by the grower.)
+  final String? family;
+
   /// Bundled identifiers of the linked species, used to derive verified
   /// "learn more" reference links (GBIF/Wikipedia/Wikispecies); null when no
   /// species is linked or the catalog entry lacks the id.
@@ -506,6 +512,7 @@ class VarietyDetail extends Equatable {
     notes,
     speciesId,
     scientificName,
+    family,
     gbifKey,
     wikidataQid,
     viabilityYears,
@@ -1022,6 +1029,7 @@ class VarietyRepository {
     if (v == null) return null;
 
     String? scientificName;
+    String? family;
     int? viabilityYears;
     int? gbifKey;
     String? wikidataQid;
@@ -1030,6 +1038,7 @@ class VarietyRepository {
         _db.species,
       )..where((s) => s.id.equals(v.speciesId!))).getSingleOrNull();
       scientificName = species?.scientificName;
+      family = species?.family;
       viabilityYears = species?.viabilityYears;
       gbifKey = species?.gbifKey;
       wikidataQid = species?.wikidataQid;
@@ -1119,6 +1128,7 @@ class VarietyRepository {
       notes: v.notes,
       speciesId: v.speciesId,
       scientificName: scientificName,
+      family: family,
       gbifKey: gbifKey,
       wikidataQid: wikidataQid,
       viabilityYears: viabilityYears,