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/test/data/species_repository_test.dart

@@ -1,4 +1,5 @@
 import 'package:commons_core/commons_core.dart';
+import 'package:drift/drift.dart' show Value;
 import 'package:flutter_test/flutter_test.dart';
 import 'package:tane/data/species_catalog.dart';
 import 'package:tane/data/species_repository.dart';
@@ -49,6 +50,65 @@ void main() {
     },
   );
 
+  test('parseSpeciesCatalog reads gbif and wikidata identifiers', () {
+    const json = '''
+    {"version":3,"species":[
+      {"scientific_name":"Zea mays","gbif_key":5290052,"wikidata_qid":"Q11575"},
+      {"scientific_name":"Unknown sp."}
+    ]}''';
+    final seeds = parseSpeciesCatalog(json);
+    expect(seeds.first.gbifKey, 5290052);
+    expect(seeds.first.wikidataQid, 'Q11575');
+    // Missing identifiers stay null, they are optional.
+    expect(seeds.last.gbifKey, isNull);
+    expect(seeds.last.wikidataQid, isNull);
+  });
+
+  test('seedBundled persists gbif and wikidata identifiers', () async {
+    await repo.seedBundled(const [
+      SpeciesSeed(
+        scientificName: 'Zea mays',
+        gbifKey: 5290052,
+        wikidataQid: 'Q11575',
+      ),
+    ]);
+    final row = await db.select(db.species).getSingle();
+    expect(row.gbifKey, 5290052);
+    expect(row.wikidataQid, 'Q11575');
+  });
+
+  test(
+    'seedBundled backfills identifiers onto rows seeded before them',
+    () async {
+      // A pre-existing bundled row that predates the identifier fields.
+      await db
+          .into(db.species)
+          .insert(
+            SpeciesCompanion.insert(
+              id: 'legacy',
+              createdAt: 0,
+              updatedAt: '0',
+              lastAuthor: 'bundle',
+              scientificName: 'Zea mays',
+              isBundled: const Value(true),
+            ),
+          );
+
+      await repo.seedBundled(const [
+        SpeciesSeed(
+          scientificName: 'Zea mays',
+          gbifKey: 5290052,
+          wikidataQid: 'Q11575',
+        ),
+      ]);
+
+      final rows = await db.select(db.species).get();
+      expect(rows.single.id, 'legacy'); // same row, not a duplicate
+      expect(rows.single.gbifKey, 5290052);
+      expect(rows.single.wikidataQid, 'Q11575');
+    },
+  );
+
   test('seedBundled inserts species and is idempotent', () async {
     await repo.seedBundled(_seeds);
     await repo.seedBundled(_seeds); // second run must not duplicate