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_repository.dart

@@ -10,6 +10,8 @@ class SpeciesSeed {
     this.family,
     this.commonNames = const {},
     this.viabilityYears,
+    this.gbifKey,
+    this.wikidataQid,
   });
 
   final String scientificName;
@@ -20,6 +22,13 @@ class SpeciesSeed {
 
   /// Typical seed longevity in years (bundled reference data); null if unknown.
   final int? viabilityYears;
+
+  /// GBIF backbone taxon key; null if unknown. Feeds the derived reference link.
+  final int? gbifKey;
+
+  /// Wikidata item id (e.g. `Q23501`); null if unknown. Feeds the derived
+  /// Wikipedia (locale-aware) reference link.
+  final String? wikidataQid;
 }
 
 /// A catalog match surfaced to the UI (with a best common name for the locale).
@@ -63,13 +72,28 @@ class SpeciesRepository {
                   ..where((s) => s.scientificName.equals(seed.scientificName)))
                 .getSingleOrNull();
         if (existing != null) {
-          // Backfill bundled reference data added after the row was seeded.
-          if (existing.viabilityYears == null && seed.viabilityYears != null) {
+          // Backfill bundled reference data added after the row was seeded, so
+          // it reaches installs seeded before these fields were bundled. Each
+          // field is only written when the row still lacks it.
+          final backfill = SpeciesCompanion(
+            viabilityYears:
+                existing.viabilityYears == null && seed.viabilityYears != null
+                ? Value(seed.viabilityYears)
+                : const Value.absent(),
+            gbifKey: existing.gbifKey == null && seed.gbifKey != null
+                ? Value(seed.gbifKey)
+                : const Value.absent(),
+            wikidataQid:
+                existing.wikidataQid == null && seed.wikidataQid != null
+                ? Value(seed.wikidataQid)
+                : const Value.absent(),
+          );
+          if (backfill.viabilityYears.present ||
+              backfill.gbifKey.present ||
+              backfill.wikidataQid.present) {
             await (_db.update(
               _db.species,
-            )..where((s) => s.id.equals(existing.id))).write(
-              SpeciesCompanion(viabilityYears: Value(seed.viabilityYears)),
-            );
+            )..where((s) => s.id.equals(existing.id))).write(backfill);
           }
           continue;
         }
@@ -87,6 +111,8 @@ class SpeciesRepository {
                 family: Value(seed.family),
                 isBundled: const Value(true),
                 viabilityYears: Value(seed.viabilityYears),
+                gbifKey: Value(seed.gbifKey),
+                wikidataQid: Value(seed.wikidataQid),
               ),
             );