feat(inventory): filter by category and lot form + a11y polish

Add filter chips above the inventory list, one per category in use and
one per lot form actually held; results apply search ∧ category ∧ form.
An active filter that empties the list shows a distinct 'no matches'
state and a clear-filters button. VarietyListItem now carries the set of
lot forms it holds (one aggregate query), and the stream re-emits on lot
changes.

Accessibility: category headers use the text theme so they honour the
system font scale; the list avatar is excluded from semantics (the tile
title already announces the name); the edit action uses the green action
colour (≥3:1 on the canvas, up from 2.62:1). Add category/form/clear
filter tests and a tap-target-size guideline test.

apps/app_seeds/test/ui/inventory_list_screen_test.dart

@@ -1,8 +1,10 @@
 import 'dart:typed_data';
 
+import 'package:commons_core/commons_core.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:tane/db/database.dart';
+import 'package:tane/db/enums.dart';
 import 'package:tane/i18n/strings.g.dart';
 import 'package:tane/ui/inventory_list_screen.dart';
 
@@ -48,7 +50,8 @@ void main() {
       await tester.pumpAndSettle();
 
       expect(find.text('Grandma tomato'), findsOneWidget);
-      expect(find.text('Solanaceae'), findsOneWidget); // category header
+      // The category now appears both as a group header and a filter chip.
+      expect(find.text('Solanaceae'), findsWidgets);
       await disposeTree(tester);
     },
   );
@@ -71,6 +74,120 @@ void main() {
     await disposeTree(tester);
   });
 
+  testWidgets('a category chip filters the list to that category', (
+    tester,
+  ) async {
+    final repo = newTestRepository(db);
+    await repo.addQuickVariety(label: 'Tomato', category: 'Solanaceae');
+    await repo.addQuickVariety(label: 'Bean', category: 'Fabaceae');
+
+    await tester.pumpWidget(
+      wrapScreen(repository: repo, child: const InventoryListScreen()),
+    );
+    await tester.pumpAndSettle();
+
+    await tester.tap(
+      find.byKey(const Key('inventory.filter.category.Solanaceae')),
+    );
+    await tester.pumpAndSettle();
+
+    expect(find.text('Tomato'), findsOneWidget);
+    expect(find.text('Bean'), findsNothing);
+    await disposeTree(tester);
+  });
+
+  testWidgets('a form chip filters the list to that lot form', (tester) async {
+    final repo = newTestRepository(db);
+    const oneUnit = Quantity(kind: QuantityKind.packet, count: 1);
+    await repo.addQuickVariety(
+      label: 'SeedOnly',
+      quantity: oneUnit,
+      lotType: LotType.seed,
+    );
+    await repo.addQuickVariety(
+      label: 'PlantOnly',
+      quantity: oneUnit,
+      lotType: LotType.plant,
+    );
+
+    await tester.pumpWidget(
+      wrapScreen(repository: repo, child: const InventoryListScreen()),
+    );
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.byKey(const Key('inventory.filter.type.seed')));
+    await tester.pumpAndSettle();
+
+    expect(find.text('SeedOnly'), findsOneWidget);
+    expect(find.text('PlantOnly'), findsNothing);
+    await disposeTree(tester);
+  });
+
+  testWidgets('clearing filters restores the full list', (tester) async {
+    final repo = newTestRepository(db);
+    await repo.addQuickVariety(label: 'Tomato', category: 'Solanaceae');
+    await repo.addQuickVariety(label: 'Bean', category: 'Fabaceae');
+
+    await tester.pumpWidget(
+      wrapScreen(repository: repo, child: const InventoryListScreen()),
+    );
+    await tester.pumpAndSettle();
+
+    await tester.tap(
+      find.byKey(const Key('inventory.filter.category.Fabaceae')),
+    );
+    await tester.pumpAndSettle();
+    expect(find.text('Tomato'), findsNothing);
+
+    await tester.tap(find.byKey(const Key('inventory.filter.clear')));
+    await tester.pumpAndSettle();
+    expect(find.text('Tomato'), findsOneWidget);
+    expect(find.text('Bean'), findsOneWidget);
+    await disposeTree(tester);
+  });
+
+  testWidgets('a filter that hides everything shows the no-matches state', (
+    tester,
+  ) async {
+    final repo = newTestRepository(db);
+    const oneUnit = Quantity(kind: QuantityKind.packet, count: 1);
+    await repo.addQuickVariety(
+      label: 'SeedOnly',
+      quantity: oneUnit,
+      lotType: LotType.seed,
+    );
+
+    await tester.pumpWidget(
+      wrapScreen(repository: repo, child: const InventoryListScreen()),
+    );
+    await tester.pumpAndSettle();
+
+    // Search excludes the only item, so the list empties under an active query.
+    await tester.enterText(
+      find.byKey(const Key('inventory.search')),
+      'zzz-nope',
+    );
+    await tester.tap(find.byKey(const Key('inventory.filter.type.seed')));
+    await tester.pumpAndSettle();
+
+    expect(find.text('No seeds match your filters.'), findsOneWidget);
+    await disposeTree(tester);
+  });
+
+  testWidgets('meets the tap-target size guideline', (tester) async {
+    final repo = newTestRepository(db);
+    await repo.addQuickVariety(label: 'Tomato', category: 'Solanaceae');
+
+    await tester.pumpWidget(
+      wrapScreen(repository: repo, child: const InventoryListScreen()),
+    );
+    await tester.pumpAndSettle();
+
+    await expectLater(tester, meetsGuideline(androidTapTargetGuideline));
+    await expectLater(tester, meetsGuideline(iOSTapTargetGuideline));
+    await disposeTree(tester);
+  });
+
   testWidgets('renders in Spanish when the locale is es', (tester) async {
     final repo = newTestRepository(db);
     await tester.pumpWidget(