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/lib/i18n/strings_en.g.dart

@@ -268,6 +268,12 @@ class Translations$inventory$en {
 	/// en: 'No seeds yet. Tap + to add your first.'
 	String get empty => 'No seeds yet. Tap + to add your first.';
 
+	/// en: 'No seeds match your filters.'
+	String get noMatches => 'No seeds match your filters.';
+
+	/// en: 'Clear filters'
+	String get clearFilters => 'Clear filters';
+
 	/// en: 'Uncategorized'
 	String get uncategorized => 'Uncategorized';
 }
@@ -984,6 +990,8 @@ extension on Translations {
 			'inventory.title' => 'Inventory',
 			'inventory.searchHint' => 'Search seeds',
 			'inventory.empty' => 'No seeds yet. Tap + to add your first.',
+			'inventory.noMatches' => 'No seeds match your filters.',
+			'inventory.clearFilters' => 'Clear filters',
 			'inventory.uncategorized' => 'Uncategorized',
 			'quickAdd.title' => 'Add a seed',
 			'quickAdd.labelField' => 'Name',