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/variety_repository.dart

@@ -301,6 +301,8 @@ class VarietyDetail extends Equatable {
     this.notes,
     this.speciesId,
     this.scientificName,
+    this.gbifKey,
+    this.wikidataQid,
     this.viabilityYears,
     this.isOrganic = false,
     this.needsReproduction = false,
@@ -322,6 +324,12 @@ class VarietyDetail extends Equatable {
   final String? speciesId;
   final String? scientificName;
 
+  /// Bundled identifiers of the linked species, used to derive verified
+  /// "learn more" reference links (GBIF/Wikipedia/Wikispecies); null when no
+  /// species is linked or the catalog entry lacks the id.
+  final int? gbifKey;
+  final String? wikidataQid;
+
   /// Grower-declared organic ("eco") provenance.
   final bool isOrganic;
 
@@ -363,6 +371,8 @@ class VarietyDetail extends Equatable {
     notes,
     speciesId,
     scientificName,
+    gbifKey,
+    wikidataQid,
     viabilityYears,
     isOrganic,
     needsReproduction,
@@ -804,12 +814,16 @@ class VarietyRepository {
 
     String? scientificName;
     int? viabilityYears;
+    int? gbifKey;
+    String? wikidataQid;
     if (v.speciesId != null) {
       final species = await (_db.select(
         _db.species,
       )..where((s) => s.id.equals(v.speciesId!))).getSingleOrNull();
       scientificName = species?.scientificName;
       viabilityYears = species?.viabilityYears;
+      gbifKey = species?.gbifKey;
+      wikidataQid = species?.wikidataQid;
     }
 
     final lots =
@@ -896,6 +910,8 @@ class VarietyRepository {
       notes: v.notes,
       speciesId: v.speciesId,
       scientificName: scientificName,
+      gbifKey: gbifKey,
+      wikidataQid: wikidataQid,
       viabilityYears: viabilityYears,
       isOrganic: v.isOrganic,
       needsReproduction: v.needsReproduction,