feat(messages): unread badges + OS notification for private messages

Private messages (NIP-17) arrived in the foreground with no signal: no
unread count, no badge, no OS notification. Hook both into the single
InboxService.ingest choke point.

- UnreadService: per-peer "last read" in the keystore (timestamps+pubkey
  only, no message text), live count via a changes stream, active-peer
  suppression so the open chat never badges or notifies.
- UnreadBadge: reusable, RTL-aware (Flutter Badge) — on the home hamburger,
  the drawer "Chat" item, and per-conversation in the messages list.
- Mark-read on chat open (ChatScreen).
- NotificationService over flutter_local_notifications: generic
  "New message from <name>" (no message text, for privacy), payload = pubkey,
  tap opens /chat/:pubkey. No-op on web/Windows; Android POST_NOTIFICATIONS.
- i18n notifications.newMessageFrom (en/es/pt/ast).

Background/push stays out of scope (foreground-only by design).

Tests: UnreadService, NotificationService (mock plugin), InboxService hooks
(new peer notifies/counts; duplicate, own, and open-chat do not), and a
UnreadBadge widget test. dart analyze clean; commons_core green.

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

@@ -214,8 +214,18 @@
     "anyMonth": "Cualquier mes",
     "noDate": "Indicar fecha de cosecha",
     "monthNames": [
-      "enero", "febrero", "marzo", "abril", "mayo", "junio",
-      "julio", "agosto", "septiembre", "octubre", "noviembre", "diciembre"
+      "enero",
+      "febrero",
+      "marzo",
+      "abril",
+      "mayo",
+      "junio",
+      "julio",
+      "agosto",
+      "septiembre",
+      "octubre",
+      "noviembre",
+      "diciembre"
     ]
   },
   "lotType": {
@@ -330,30 +340,102 @@
     "some": "algunas",
     "plenty": "muchas",
     "pinch": "una pizca",
-    "handful": { "singular": "puñado", "plural": "puñados" },
-    "teaspoon": { "singular": "cucharadita", "plural": "cucharaditas" },
-    "spoon": { "singular": "cuchara", "plural": "cucharas" },
-    "cup": { "singular": "taza", "plural": "tazas" },
-    "jar": { "singular": "bote", "plural": "botes" },
-    "sack": { "singular": "saco", "plural": "sacos" },
-    "packet": { "singular": "sobre", "plural": "sobres" },
-    "cob": { "singular": "mazorca", "plural": "mazorcas" },
-    "pod": { "singular": "vaina", "plural": "vainas" },
-    "ear": { "singular": "espiga", "plural": "espigas" },
-    "head": { "singular": "cabezuela", "plural": "cabezuelas" },
-    "fruit": { "singular": "fruto", "plural": "frutos" },
-    "bulb": { "singular": "bulbo", "plural": "bulbos" },
-    "tuber": { "singular": "tubérculo", "plural": "tubérculos" },
-    "seedHead": { "singular": "cabeza de semillas", "plural": "cabezas de semillas" },
-    "bunch": { "singular": "manojo", "plural": "manojos" },
-    "plant": { "singular": "planta", "plural": "plantas" },
-    "pot": { "singular": "maceta", "plural": "macetas" },
-    "tray": { "singular": "bandeja", "plural": "bandejas" },
-    "seedling": { "singular": "plántula", "plural": "plántulas" },
-    "tree": { "singular": "árbol", "plural": "árboles" },
-    "cutting": { "singular": "esqueje", "plural": "esquejes" },
-    "grams": { "singular": "gramo", "plural": "gramos" },
-    "count": { "singular": "semilla", "plural": "semillas" }
+    "handful": {
+      "singular": "puñado",
+      "plural": "puñados"
+    },
+    "teaspoon": {
+      "singular": "cucharadita",
+      "plural": "cucharaditas"
+    },
+    "spoon": {
+      "singular": "cuchara",
+      "plural": "cucharas"
+    },
+    "cup": {
+      "singular": "taza",
+      "plural": "tazas"
+    },
+    "jar": {
+      "singular": "bote",
+      "plural": "botes"
+    },
+    "sack": {
+      "singular": "saco",
+      "plural": "sacos"
+    },
+    "packet": {
+      "singular": "sobre",
+      "plural": "sobres"
+    },
+    "cob": {
+      "singular": "mazorca",
+      "plural": "mazorcas"
+    },
+    "pod": {
+      "singular": "vaina",
+      "plural": "vainas"
+    },
+    "ear": {
+      "singular": "espiga",
+      "plural": "espigas"
+    },
+    "head": {
+      "singular": "cabezuela",
+      "plural": "cabezuelas"
+    },
+    "fruit": {
+      "singular": "fruto",
+      "plural": "frutos"
+    },
+    "bulb": {
+      "singular": "bulbo",
+      "plural": "bulbos"
+    },
+    "tuber": {
+      "singular": "tubérculo",
+      "plural": "tubérculos"
+    },
+    "seedHead": {
+      "singular": "cabeza de semillas",
+      "plural": "cabezas de semillas"
+    },
+    "bunch": {
+      "singular": "manojo",
+      "plural": "manojos"
+    },
+    "plant": {
+      "singular": "planta",
+      "plural": "plantas"
+    },
+    "pot": {
+      "singular": "maceta",
+      "plural": "macetas"
+    },
+    "tray": {
+      "singular": "bandeja",
+      "plural": "bandejas"
+    },
+    "seedling": {
+      "singular": "plántula",
+      "plural": "plántulas"
+    },
+    "tree": {
+      "singular": "árbol",
+      "plural": "árboles"
+    },
+    "cutting": {
+      "singular": "esqueje",
+      "plural": "esquejes"
+    },
+    "grams": {
+      "singular": "gramo",
+      "plural": "gramos"
+    },
+    "count": {
+      "singular": "semilla",
+      "plural": "semillas"
+    }
   },
   "market": {
     "title": "Semillas cerca de ti",
@@ -438,5 +520,8 @@
     "vouch": "Conozco a esta persona",
     "vouched": "Avalas a esta persona",
     "circle": "En tu círculo"
+  },
+  "notifications": {
+    "newMessageFrom": "Nuevo mensaje de {name}"
   }
 }