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/assets/catalog/seed_saving.json

@@ -1,6 +1,11 @@
 {
   "version": 1,
-  "note": "Curated seed-saving guidance (public-domain horticultural knowledge, e.g. Ashworth 'Seed to Seed', Seed Savers Exchange). Keyed by botanical family (defaults) with per-species/genus overrides that win. Distances in metres are conservative home-garden ranges for keeping a variety reasonably true; plant counts keep enough genetic diversity. `note` is a locale-keyed map, extensible to any language. This is a starter set, not a ceiling.",
+  "note": "Curated seed-saving guidance. Values are widely-published horticultural FACTS (isolation distances, pollination habit, population sizes) — not copied text — drawn from the sources below and cross-checked for consistency. Keyed by botanical family (defaults) with per-species/genus overrides that win. Distances in metres are conservative home-garden ranges for keeping a variety reasonably true; plant counts keep enough genetic diversity. `note` is a locale-keyed map, extensible to any language. Advisory only — adapt to local climate. A starter set, not a ceiling.",
+  "sources": [
+    { "title": "Seed to Seed", "author": "Suzanne Ashworth", "publisher": "Seed Savers Exchange" },
+    { "title": "Seed Savers Exchange", "url": "https://seedsavers.org" },
+    { "title": "Organic Seed Alliance", "url": "https://seedalliance.org" }
+  ],
   "families": {
     "Solanaceae": { "lifeCycle": "annual", "pollination": "self", "vector": "self", "isolationMinM": 3, "isolationMaxM": 15, "minPlants": 1, "recommendedPlants": 6, "processing": "wet", "difficulty": "easy" },
     "Fabaceae": { "lifeCycle": "annual", "pollination": "self", "vector": "self", "isolationMinM": 3, "isolationMaxM": 20, "minPlants": 1, "recommendedPlants": 10, "processing": "dry", "difficulty": "easy" },