polish(ux): drop the checkmark on selected filter chips

The tick overlapped the leading icon on selected chips, reading as a
confusing blob. The solid fill already signals 'on', so hide the
checkmark. Also make the selected label reliably white via an explicit
per-chip style: the global ChipTheme's secondaryLabelStyle was not
applied to FilterChips, leaving dark text on green. Plain attribute/
market chips now share a PlainFilterChip widget; swatch and month chips
just drop their tick.

apps/app_seeds/lib/ui/market_screen.dart

@@ -13,6 +13,7 @@ import '../services/social_service.dart';
 import '../services/social_settings.dart';
 import '../state/offers_cubit.dart';
 import 'edge_fade.dart';
+import 'filter_chips.dart';
 import 'market_widgets.dart';
 import 'theme.dart';
 
@@ -488,28 +489,24 @@ class _MarketFilterBar extends StatelessWidget {
 
     final chips = <Widget>[
       if (hasOrganic)
-        FilterChip(
+        PlainFilterChip(
           key: const Key('market.filter.organic'),
-          avatar: Icon(
-            Icons.eco,
-            size: 18,
-            color: state.organicOnly ? Colors.white : seedGreen,
-          ),
-          label: Text(t.editVariety.organic),
+          icon: Icons.eco,
+          label: t.editVariety.organic,
           selected: state.organicOnly,
           onSelected: (_) => cubit.toggleOrganicOnly(),
         ),
       for (final type in types)
-        FilterChip(
+        PlainFilterChip(
           key: Key('market.filter.type.${type.name}'),
-          label: Text(offerTypeLabel(t, type)),
+          label: offerTypeLabel(t, type),
           selected: state.typeFilter.contains(type),
           onSelected: (_) => cubit.toggleType(type),
         ),
       for (final category in categories)
-        FilterChip(
+        PlainFilterChip(
           key: Key('market.filter.category.$category'),
-          label: Text(category),
+          label: category,
           selected: state.categoryFilter.contains(category),
           onSelected: (_) => cubit.toggleCategory(category),
         ),