feat(plantare): surface product link + dates; spec the bilateral record

The Plantaré screen stored madeOn/dueBy/varietyId but showed none of them,
so it felt half-built. Surface what's already there (no schema change):

- watchPlantareViews() joins each commitment with its variety label
- tile shows the made-on date, a "Return by {date}" line (amber + "overdue"
  when an open promise is past due, via new seedWarning colour), the variety
  name, and taps through to /variety/:id
- add sheet gains an optional return-by date picker (createPlantare already
  took dueBy)
- variety detail shows a read-only commitments section (hidden when empty,
  no add button — honours the single hand-over door)
- i18n en/es/pt/ast; tests for the join, dueBy round-trip, tile, and section

Also specs the deferred two-sided record in docs/design/plantare-bilateral.md
(Nostr pubkey counterparty, PlantareTransport propose->accept->counter-sign,
deferred key/signature/movement columns, provenance DAG, reputation anchor),
with a faithful transcription of the paper Plantaré v0.4 (BAH-Semillero 2009,
CC-BY-SA). Cross-linked from data-model §2.7 and sharing-model §6.

apps/app_seeds/lib/ui/theme.dart

@@ -26,6 +26,7 @@ const seedOnSurfaceVariant = Color(0xFF5C6B52); // scientific names, secondary
 const seedMuted = Color(0xFF617057);
 const seedRating = Color(0xFFE8A200); // stars
 const seedFavorite = Color(0xFFE53935); // saved/favorite heart (pops on green)
+const seedWarning = Color(0xFFA84600); // overdue nudges (AA on white & canvas)
 
 ThemeData buildTaneTheme() {
   final scheme =