feat(calendar): "what's due this month" — dedicated screen + inventory filter

Reuses the existing per-variety crop-calendar masks (sow/transplant/
flowering/fruiting/seed-harvest) — no schema change, no migration — to
answer "qué toca este mes" across the whole inventory. Since the months
are the grower's own record, there's no hemisphere assumption.

- Repo: CalendarEntry + watchCalendar() (varieties with any recorded
  phase); VarietyListItem now carries sowMonths.
- Dedicated CalendarScreen (/calendar): a month strip (defaults to the
  current month, intl month names) and varieties grouped by phase —
  actions (sow/transplant/harvest seed) above informational (flowering/
  fruiting), each tinted, tap → variety detail; empty-month state.
- Inventory filter: a 'this month' chip (shown only when some variety
  has a calendar) keeps what sows in the current month; folded into the
  attributes group + clear-filters.
- Entry points: a live Home card + a drawer item.
- i18n calendar block + menu.calendar (en/es/pt/ast).
- Tests: calendar_test (watchCalendar, list carries sow-months, pure
  filter), calendar_screen_test (phase grouping, month switch, empty),
  plus the screen added to the small-screen overflow guard.

apps/app_seeds/lib/i18n/es.i18n.json

@@ -1,4 +1,10 @@
 {
+  "calendar": {
+    "title": "Este mes",
+    "homeSubtitle": "Qué sembrar y hacer ahora",
+    "filterChip": "Este mes",
+    "nothing": "Nada anotado para {month}."
+  },
   "app": {
     "title": "Tanemaki"
   },
@@ -39,6 +45,7 @@
     "following": "Siguiendo",
     "plantares": "Plantares",
     "sales": "Ventas",
+    "calendar": "Calendario",
     "settings": "Ajustes"
   },
   "settings": {