feat(plantare): reproduction-commitment data layer (schema v9)

The Plantare — a promise to reproduce seed and return some (data-model §2.7,
the seed-domain Pledge with return_kind=similar). NOT a sale. Local-first
v1: your honest ledger of commitments (from/to a person by name); the
bilateral signed cross-party form is a later social-layer phase.

- New Plantares table (SyncColumns): varietyId, direction (iReturn/owedToMe),
  counterparty, owedDescription, madeOn, dueBy, status (open/returned/
  forgiven), settledOn, note. schemaVersion 8 -> 9 with a guarded createTable
  migration; schema exported + migration-test helper regenerated.
- VarietyRepository: createPlantare / watchPlantares / watchPlantaresForVariety
  / setPlantareStatus / deletePlantare (soft-delete, CRDT-stamped).
- Included in backups + sync: InventorySnapshot + JSON codec (round-trips
  isDeleted) + exportInventory/exportForSync/importInventory, so commitments
  survive restore and replicate LWW like every other row.

Tests: v1..v8 -> v9 migration + fresh v9; repo create/list/settle/reopen/
delete; and a backup round-trip preserving a commitment. 13 green.

UI (detail section + Plantares screen) follows.

apps/app_seeds/test/db/schema/schema.dart

@@ -12,6 +12,7 @@ import 'schema_v5.dart' as v5;
 import 'schema_v6.dart' as v6;
 import 'schema_v7.dart' as v7;
 import 'schema_v8.dart' as v8;
+import 'schema_v9.dart' as v9;
 
 class GeneratedHelper implements SchemaInstantiationHelper {
   @override
@@ -33,10 +34,12 @@ class GeneratedHelper implements SchemaInstantiationHelper {
         return v7.DatabaseAtV7(db);
       case 8:
         return v8.DatabaseAtV8(db);
+      case 9:
+        return v9.DatabaseAtV9(db);
       default:
         throw MissingSchemaException(version, versions);
     }
   }
 
-  static const versions = const [1, 2, 3, 4, 5, 6, 7, 8];
+  static const versions = const [1, 2, 3, 4, 5, 6, 7, 8, 9];
 }