feat(seed-saving): source attribution + advisory note

Record where the guidance comes from (copyright/attribution) and make
clear it is general, not local gospel — kept light:
- seed_saving.json gains a top-level sources list (Seed to Seed / Seed
  Savers Exchange / Organic Seed Alliance); parsed into
  SeedSavingData.sources, exposed via SeedSavingCatalog.sources.
- The detail section shows a small muted footer: an italic 'advisory —
  adapt to your climate' line plus a 'Source: …' credit.
- i18n seedSaving.advisory + sourcePrefix (en/es/pt/ast).
- Tests: asset carries sources; the section renders advisory + credit.

apps/app_seeds/lib/i18n/strings_es.g.dart

@@ -114,6 +114,8 @@ class _Translations$seedSaving$es extends Translations$seedSaving$en {
 	@override String get diffEasy => 'Fácil';
 	@override String get diffMedium => 'Media';
 	@override String get diffHard => 'Difícil';
+	@override String get advisory => 'Orientativo — adáptalo a tu clima y variedad.';
+	@override String get sourcePrefix => 'Fuente';
 }
 
 // Path: calendar
@@ -1286,6 +1288,8 @@ extension on TranslationsEs {
 			'seedSaving.diffEasy' => 'Fácil',
 			'seedSaving.diffMedium' => 'Media',
 			'seedSaving.diffHard' => 'Difícil',
+			'seedSaving.advisory' => 'Orientativo — adáptalo a tu clima y variedad.',
+			'seedSaving.sourcePrefix' => 'Fuente',
 			'calendar.title' => 'Este mes',
 			'calendar.filterChip' => 'Este mes',
 			'calendar.nothing' => ({required Object month}) => 'Nada anotado para ${month}.',