feat(block2): profiles — your identity card + name/about (NIP-01 kind:0)

Drawer 'Profile' is now live.
- commons_core: ProfileTransport + UserProfile + NostrProfileTransport (kind:0
  publish/fetch), exposed as SocialSession.profile. Round-trip tested against the
  in-process relay (fast dart test).
- app: ProfileStore (local name/about, keystore) + ProfileScreen — shows your
  shareable npub with copy, edits display name + 'about', saves locally and (when
  online) publishes kind:0 so peers can recognise you instead of a raw key.
- Drawer 'Profile' -> /profile (gated like Market/Chat).
- i18n en/es/pt. ProfileStore + profile transport covered by plain/dart tests.

Analyzer clean (both packages).

apps/app_seeds/lib/i18n/en.i18n.json

@@ -361,6 +361,19 @@
     "locationFailed": "Couldn't get your location — check that location is on and the permission is granted",
     "queued": "Saved — we'll share these when you're connected"
   },
+  "profile": {
+    "title": "Your profile",
+    "name": "Display name",
+    "nameHint": "How others see you",
+    "about": "About",
+    "aboutHint": "A short line — what you grow, where",
+    "yourId": "Your identity",
+    "idHelp": "Share this so people can recognise you",
+    "copy": "Copy",
+    "copied": "Copied",
+    "save": "Save",
+    "saved": "Profile saved"
+  },
   "chatList": {
     "title": "Messages",
     "empty": "No conversations yet. Message someone from the market."