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/lib/data/variety_repository.dart

@@ -8,14 +8,22 @@ import '../db/enums.dart';
 
 /// A lightweight row for the inventory list (only what the list renders).
 class VarietyListItem extends Equatable {
-  const VarietyListItem({required this.id, required this.label, this.category});
+  const VarietyListItem({
+    required this.id,
+    required this.label,
+    this.category,
+    this.photo,
+  });
 
   final String id;
   final String label;
   final String? category;
 
+  /// First photo (encrypted BLOB) for the avatar, or null → show an initial.
+  final Uint8List? photo;
+
   @override
-  List<Object?> get props => [id, label, category];
+  List<Object?> get props => [id, label, category, photo];
 }
 
 /// One germination test on a lot; [rate] is derived (0..1), null when it can't
@@ -135,7 +143,8 @@ class VarietyRepository {
   final int Function() _now;
   Hlc _clock;
 
-  /// Emits the non-deleted inventory, ordered by category then label.
+  /// Emits the non-deleted inventory, ordered by category then label, each with
+  /// its first photo for the avatar.
   Stream<List<VarietyListItem>> watchInventory() {
     final query = _db.select(_db.varieties)
       ..where((v) => v.isDeleted.equals(false))
@@ -143,14 +152,41 @@ class VarietyRepository {
         (v) => OrderingTerm(expression: v.category),
         (v) => OrderingTerm(expression: v.label),
       ]);
-    return query.watch().map(
-      (rows) => rows
+    return query.watch().asyncMap((rows) async {
+      final photos = await _firstPhotosFor(rows.map((v) => v.id).toList());
+      return rows
           .map(
-            (v) =>
-                VarietyListItem(id: v.id, label: v.label, category: v.category),
+            (v) => VarietyListItem(
+              id: v.id,
+              label: v.label,
+              category: v.category,
+              photo: photos[v.id],
+            ),
           )
-          .toList(),
-    );
+          .toList();
+    });
+  }
+
+  /// Loads the first photo BLOB for each of [varietyIds] (one query).
+  Future<Map<String, Uint8List>> _firstPhotosFor(
+    List<String> varietyIds,
+  ) async {
+    if (varietyIds.isEmpty) return const {};
+    final rows =
+        await (_db.select(_db.attachments)..where(
+              (a) =>
+                  a.parentId.isIn(varietyIds) &
+                  a.parentType.equalsValue(ParentType.variety) &
+                  a.kind.equalsValue(AttachmentKind.photo) &
+                  a.isDeleted.equals(false),
+            ))
+            .get();
+    final byVariety = <String, Uint8List>{};
+    for (final row in rows) {
+      final bytes = row.bytes;
+      if (bytes != null) byVariety.putIfAbsent(row.parentId, () => bytes);
+    }
+    return byVariety;
   }
 
   /// The 20-second quick-add: a [label] (required) plus an optional [category],