feat(species): derived verified reference links (GBIF/Wikipedia/Wikispecies)

Add a read-only "Learn more" section on the variety detail that surfaces
verified external references for the linked species, built deterministically
from bundled identifiers — no titles bundled, no network, offline-first:

- GBIF taxon page from the backbone key
- Wikipedia via Wikidata Special:GoToLinkedPage (locale-aware, RTL-safe,
  falls back to the Wikidata item when a language lacks the article)
- Wikispecies from the scientific name

Enrich the bundled catalog (species.json v3) with gbif_key + wikidata_qid for
all 14 species, cross-checked (each QID carries GBIF ID P846 = the key).
Schema already had the columns; seedBundled now persists and backfills them.

The grower's own manual links stay but are demoted (progressive disclosure):
the section only shows when links exist and "Add link" is a low-emphasis
button, since hand-adding a link is the rarer power move.

Pure-Dart link builder is unit-tested; repo persistence/backfill and the
detail-screen section are covered too.

apps/app_seeds/lib/data/species_catalog.dart

@@ -20,6 +20,8 @@ List<SpeciesSeed> parseSpeciesCatalog(String jsonString) {
       family: e['family'] as String?,
       commonNames: common,
       viabilityYears: (e['viability_years'] as num?)?.toInt(),
+      gbifKey: (e['gbif_key'] as num?)?.toInt(),
+      wikidataQid: e['wikidata_qid'] as String?,
     );
   }).toList();
 }