perf(inventory): lazy list, photo thumbnails, indexes, debounced reload

Scale the local inventory to 10k+ varieties:
- Render the list with ListView.builder over a flattened header/item model
  instead of building every tile upfront.
- Store a small regenerable JPEG thumbnail per photo (schema v14) and use it
  for the 48px list avatar; full bytes stay for offer image hosting. Existing
  photos are backfilled lazily at startup. Thumbnail is local-only (excluded
  from CRDT sync and backups by the JSON codec).
- Add indexes on varieties(is_deleted,is_draft), attachments(parent_type,
  parent_id,kind), lots(variety_id) via @TableIndex.
- Debounce watchInventoryView (~250ms) so a burst of table writes triggers one
  reload, not seven.
- cacheWidth/cacheHeight on the list avatar decode.
- Scale test raised 3k -> 10k; migration test v13 -> v14.

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

@@ -17,6 +17,7 @@ import 'schema_v10.dart' as v10;
 import 'schema_v11.dart' as v11;
 import 'schema_v12.dart' as v12;
 import 'schema_v13.dart' as v13;
+import 'schema_v14.dart' as v14;
 
 class GeneratedHelper implements SchemaInstantiationHelper {
   @override
@@ -48,10 +49,12 @@ class GeneratedHelper implements SchemaInstantiationHelper {
         return v12.DatabaseAtV12(db);
       case 13:
         return v13.DatabaseAtV13(db);
+      case 14:
+        return v14.DatabaseAtV14(db);
       default:
         throw MissingSchemaException(version, versions);
     }
   }
 
-  static const versions = const [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13];
+  static const versions = const [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14];
 }