Closes the profile loop — peers now appear by name, not a raw key.
- ProfileCache: keystore-backed cache of peers' published display names (works
offline) + shortPubkey() fallback.
- Chat: the app bar shows the peer's name (cached first, then freshened from
their kind:0 over the session); falls back to a short key.
- Inbox: each conversation shows the cached name, and missing names are resolved
over one session and cached.
- Wired via DI + TaneApp(profileCache).
Analyzer clean; ProfileCache covered by a plain test.
