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/data/inventory_scale_test.dart

@@ -19,8 +19,8 @@ void main() {
   });
   tearDown(() => db.close());
 
-  test('the inventory view loads 3000 varieties quickly', () async {
-    const count = 3000;
+  test('the inventory view loads 10000 varieties quickly', () async {
+    const count = 10000;
     for (var i = 0; i < count; i++) {
       final id = await repo.addQuickVariety(
         label: 'Variety $i',
@@ -43,11 +43,12 @@ void main() {
     sw.stop();
 
     expect(view.items, hasLength(count));
-    // Generous ceiling for CI; typical local runs are well under 500ms. The
-    // point is to catch an accidental N+1 regression, not to micro-benchmark.
+    // Generous ceiling for CI (the point is to catch an N+1 regression, not to
+    // micro-benchmark). Includes the ~250ms debounce on the first emit; typical
+    // local runs are well under 2s for 10k rows with the v14 indexes.
     expect(
       sw.elapsedMilliseconds,
-      lessThan(3000),
+      lessThan(6000),
       reason: 'inventory view took ${sw.elapsedMilliseconds}ms for $count rows',
     );
   });

apps/app_seeds/test/db/migration_test.dart

@@ -11,19 +11,19 @@ void main() {
     verifier = SchemaVerifier(GeneratedHelper());
   });
 
-  test('freshly created database matches the exported schema v13', () async {
-    final schema = await verifier.schemaAt(13);
+  test('freshly created database matches the exported schema v14', () async {
+    final schema = await verifier.schemaAt(14);
     final db = AppDatabase(schema.newConnection());
-    await verifier.migrateAndValidate(db, 13);
+    await verifier.migrateAndValidate(db, 14);
     await db.close();
   });
 
-  // Every historical version upgrades cleanly to the current schema (v13).
-  for (var from = 1; from <= 12; from++) {
-    test('upgrades v$from → v13 and matches the fresh schema', () async {
+  // Every historical version upgrades cleanly to the current schema (v14).
+  for (var from = 1; from <= 13; from++) {
+    test('upgrades v$from → v14 and matches the fresh schema', () async {
       final connection = await verifier.startAt(from);
       final db = AppDatabase(connection);
-      await verifier.migrateAndValidate(db, 13);
+      await verifier.migrateAndValidate(db, 14);
       await db.close();
     });
   }

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];
 }