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/es.i18n.json

@@ -60,6 +60,8 @@
     "title": "Inventario",
     "searchHint": "Buscar semillas",
     "empty": "Aún no hay semillas. Toca + para añadir la primera.",
+    "noMatches": "Ninguna semilla coincide con los filtros.",
+    "clearFilters": "Quitar filtros",
     "uncategorized": "Sin categoría"
   },
   "quickAdd": {