feat(block1): photo thumbnails in the inventory list

The list showed only initials even when a variety had a photo (quick-add stores
one as an encrypted BLOB). Now the avatar shows the first photo, falling back to
the initial — matching the "foto/inicial" list spec.

- VarietyListItem carries the first photo bytes; watchInventory loads them in a
  single query per emission.
- List tile renders a MemoryImage avatar when present.

Tests: repository (photo bytes surfaced, null when none) and a widget test
(avatar replaces the initial). Full suite: 37 passing, 0 skipped.

apps/app_seeds/test/data/variety_repository_test.dart

@@ -52,6 +52,18 @@ void main() {
     },
   );
 
+  test('watchInventory carries the first photo bytes for the avatar', () async {
+    await repo.addQuickVariety(
+      label: 'With photo',
+      photoBytes: Uint8List.fromList([9, 8, 7]),
+    );
+    await repo.addQuickVariety(label: 'No photo');
+
+    final items = await repo.watchInventory().first;
+    expect(items.firstWhere((i) => i.label == 'With photo').photo, [9, 8, 7]);
+    expect(items.firstWhere((i) => i.label == 'No photo').photo, isNull);
+  });
+
   test(
     'stream is ordered by category then label and excludes soft-deleted rows',
     () async {

apps/app_seeds/test/ui/inventory_list_screen_test.dart

@@ -1,3 +1,5 @@
+import 'dart:typed_data';
+
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:tane/db/database.dart';
@@ -6,6 +8,14 @@ import 'package:tane/ui/inventory_list_screen.dart';
 
 import '../support/test_support.dart';
 
+/// A valid 1x1 transparent PNG so the avatar image decodes cleanly in tests.
+final _tinyPng = Uint8List.fromList(const [
+  137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 1, //
+  0, 0, 0, 1, 8, 6, 0, 0, 0, 31, 21, 196, 137, 0, 0, 0, 13, 73, 68, 65, 84, //
+  120, 156, 99, 250, 207, 0, 0, 0, 2, 0, 1, 226, 33, 188, 51, 0, 0, 0, 0, //
+  73, 69, 78, 68, 174, 66, 96, 130,
+]);
+
 void main() {
   late AppDatabase db;
 
@@ -75,4 +85,21 @@ void main() {
     expect(find.text('Inventario'), findsOneWidget);
     await disposeTree(tester);
   });
+
+  testWidgets(
+    'shows a photo avatar instead of the initial when a photo exists',
+    (tester) async {
+      final repo = newTestRepository(db);
+      await repo.addQuickVariety(label: 'Photographed', photoBytes: _tinyPng);
+
+      await tester.pumpWidget(
+        wrapScreen(repository: repo, child: const InventoryListScreen()),
+      );
+      await tester.pumpAndSettle();
+
+      expect(find.text('Photographed'), findsOneWidget);
+      expect(find.text('P'), findsNothing); // initial replaced by the photo
+      await disposeTree(tester);
+    },
+  );
 }