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/pt.i18n.json

@@ -211,8 +211,18 @@
     "anyMonth": "Qualquer mês",
     "noDate": "Definir data de colheita",
     "monthNames": [
-      "janeiro", "fevereiro", "março", "abril", "maio", "junho",
-      "julho", "agosto", "setembro", "outubro", "novembro", "dezembro"
+      "janeiro",
+      "fevereiro",
+      "março",
+      "abril",
+      "maio",
+      "junho",
+      "julho",
+      "agosto",
+      "setembro",
+      "outubro",
+      "novembro",
+      "dezembro"
     ]
   },
   "lotType": {
@@ -327,30 +337,102 @@
     "some": "bastantes",
     "plenty": "muitas",
     "pinch": "uma pitada",
-    "handful": { "singular": "mão-cheia", "plural": "mãos-cheias" },
-    "teaspoon": { "singular": "colher de chá", "plural": "colheres de chá" },
-    "spoon": { "singular": "colher", "plural": "colheres" },
-    "cup": { "singular": "chávena", "plural": "chávenas" },
-    "jar": { "singular": "frasco", "plural": "frascos" },
-    "sack": { "singular": "saco", "plural": "sacos" },
-    "packet": { "singular": "pacote", "plural": "pacotes" },
-    "cob": { "singular": "maçaroca", "plural": "maçarocas" },
-    "pod": { "singular": "vagem", "plural": "vagens" },
-    "ear": { "singular": "espiga", "plural": "espigas" },
-    "head": { "singular": "cabeça", "plural": "cabeças" },
-    "fruit": { "singular": "fruto", "plural": "frutos" },
-    "bulb": { "singular": "bolbo", "plural": "bolbos" },
-    "tuber": { "singular": "tubérculo", "plural": "tubérculos" },
-    "seedHead": { "singular": "capítulo", "plural": "capítulos" },
-    "bunch": { "singular": "molho", "plural": "molhos" },
-    "plant": { "singular": "planta", "plural": "plantas" },
-    "pot": { "singular": "vaso", "plural": "vasos" },
-    "tray": { "singular": "tabuleiro", "plural": "tabuleiros" },
-    "seedling": { "singular": "plântula", "plural": "plântulas" },
-    "tree": { "singular": "árvore", "plural": "árvores" },
-    "cutting": { "singular": "estaca", "plural": "estacas" },
-    "grams": { "singular": "grama", "plural": "gramas" },
-    "count": { "singular": "semente", "plural": "sementes" }
+    "handful": {
+      "singular": "mão-cheia",
+      "plural": "mãos-cheias"
+    },
+    "teaspoon": {
+      "singular": "colher de chá",
+      "plural": "colheres de chá"
+    },
+    "spoon": {
+      "singular": "colher",
+      "plural": "colheres"
+    },
+    "cup": {
+      "singular": "chávena",
+      "plural": "chávenas"
+    },
+    "jar": {
+      "singular": "frasco",
+      "plural": "frascos"
+    },
+    "sack": {
+      "singular": "saco",
+      "plural": "sacos"
+    },
+    "packet": {
+      "singular": "pacote",
+      "plural": "pacotes"
+    },
+    "cob": {
+      "singular": "maçaroca",
+      "plural": "maçarocas"
+    },
+    "pod": {
+      "singular": "vagem",
+      "plural": "vagens"
+    },
+    "ear": {
+      "singular": "espiga",
+      "plural": "espigas"
+    },
+    "head": {
+      "singular": "cabeça",
+      "plural": "cabeças"
+    },
+    "fruit": {
+      "singular": "fruto",
+      "plural": "frutos"
+    },
+    "bulb": {
+      "singular": "bolbo",
+      "plural": "bolbos"
+    },
+    "tuber": {
+      "singular": "tubérculo",
+      "plural": "tubérculos"
+    },
+    "seedHead": {
+      "singular": "capítulo",
+      "plural": "capítulos"
+    },
+    "bunch": {
+      "singular": "molho",
+      "plural": "molhos"
+    },
+    "plant": {
+      "singular": "planta",
+      "plural": "plantas"
+    },
+    "pot": {
+      "singular": "vaso",
+      "plural": "vasos"
+    },
+    "tray": {
+      "singular": "tabuleiro",
+      "plural": "tabuleiros"
+    },
+    "seedling": {
+      "singular": "plântula",
+      "plural": "plântulas"
+    },
+    "tree": {
+      "singular": "árvore",
+      "plural": "árvores"
+    },
+    "cutting": {
+      "singular": "estaca",
+      "plural": "estacas"
+    },
+    "grams": {
+      "singular": "grama",
+      "plural": "gramas"
+    },
+    "count": {
+      "singular": "semente",
+      "plural": "sementes"
+    }
   },
   "market": {
     "title": "Sementes perto de ti",
@@ -435,5 +517,8 @@
     "vouch": "Conheço esta pessoa",
     "vouched": "Avalizas esta pessoa",
     "circle": "No teu círculo"
+  },
+  "notifications": {
+    "newMessageFrom": "Nova mensagem de {name}"
   }
 }