feat(chat): usable 1:1 chat — bottom-anchored, Drift-backed, dated

- Anchor the message list to the bottom (`reverse: true`) so new messages
  stay in view instead of landing below the fold.
- Move chat history from the OS keystore (O(n²) JSON blob, silent 200-msg
  cap) to a separate encrypted Drift/SQLCipher DB (`ChatDatabase`):
  indexed append, uncapped history, dedup as a unique-key invariant. It's
  an ephemeral per-device cache, isolated from the inventory schema, its
  migrations, and its sync. No data migration (pre-release).
- Add day separators (Today/Yesterday/locale date) and a per-bubble time,
  all via ICU (12/24h per locale; Localizations locale maps Asturian →
  Spanish for intl date symbols).
- Add peer avatars (deterministic colour from the pubkey + name initial),
  surface send failures that were previously silent, and make bubble text
  selectable (addresses, links).
- New i18n keys in en/es/pt/ast; tests for grouping, formatting, avatars,
  scroll anchoring, storage and send errors.

Docs: docs/design/chat-storage.md + open-decisions.md.

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

@@ -530,7 +530,10 @@
     "empty": "Aún no hay mensajes — saluda",
     "offline": "Configura el compartir para enviar mensajes",
     "payG1": "Pagar en Ğ1",
-    "g1Copied": "Dirección Ğ1 copiada — pégala en tu cartera"
+    "g1Copied": "Dirección Ğ1 copiada — pégala en tu cartera",
+    "today": "Hoy",
+    "yesterday": "Ayer",
+    "sendError": "No se pudo enviar — revisa tu conexión"
   },
   "trust": {
     "none": "Nadie los avala aún",