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/lib/ui/inventory_list_screen.dart

@@ -582,27 +582,47 @@ class _InventoryBody extends StatelessWidget {
     }
 
     // Items arrive ordered by category then label; insert a header whenever the
-    // category changes.
-    final rows = <Widget>[];
+    // category changes. Precompute a flat row model (header or item) so the
+    // ListView can build tiles lazily — with a large inventory, building every
+    // tile upfront (the old `ListView(children:)`) stalled the first paint.
+    final rows = <_InventoryRow>[];
     String? currentCategory;
     for (final item in items) {
       final category = item.category ?? t.inventory.uncategorized;
       if (category != currentCategory) {
         currentCategory = category;
-        rows.add(_CategoryHeader(title: category));
+        rows.add(_InventoryRow.header(category));
       }
-      rows.add(
-        _VarietyTile(
-          item: item,
-          selectionMode: selectionMode,
-          selected: selectedIds.contains(item.id),
-        ),
-      );
+      rows.add(_InventoryRow.variety(item));
     }
-    return ListView(children: rows);
+    return ListView.builder(
+      itemCount: rows.length,
+      itemBuilder: (context, i) {
+        final row = rows[i];
+        final header = row.header;
+        if (header != null) {
+          return _CategoryHeader(title: header);
+        }
+        return _VarietyTile(
+          item: row.item!,
+          selectionMode: selectionMode,
+          selected: selectedIds.contains(row.item!.id),
+        );
+      },
+    );
   }
 }
 
+/// A single row in the flattened inventory list: either a category [header] or
+/// a variety [item] (exactly one is non-null).
+class _InventoryRow {
+  const _InventoryRow.header(this.header) : item = null;
+  const _InventoryRow.variety(this.item) : header = null;
+
+  final String? header;
+  final VarietyListItem? item;
+}
+
 class _CategoryHeader extends StatelessWidget {
   const _CategoryHeader({required this.title});
 
@@ -767,10 +787,21 @@ class _Avatar extends StatelessWidget {
     // Decorative: the tile title already announces the variety name, so keep
     // the thumbnail / initial out of the semantics tree.
     if (photo != null) {
+      // Decode straight to the 48px avatar size (× device pixel ratio) instead
+      // of holding the full-resolution photo in the image cache — decisive for
+      // memory with a large inventory of photographed varieties.
+      final cachePx = (48 * MediaQuery.devicePixelRatioOf(context)).round();
       return ExcludeSemantics(
         child: ClipRRect(
           borderRadius: BorderRadius.circular(8),
-          child: Image.memory(photo, width: 48, height: 48, fit: BoxFit.cover),
+          child: Image.memory(
+            photo,
+            width: 48,
+            height: 48,
+            cacheWidth: cachePx,
+            cacheHeight: cachePx,
+            fit: BoxFit.cover,
+          ),
         ),
       );
     }