feat(signer): accept bunker:// URIs, async signer permissions, NIP-46 e2e test

- SignerManager/SignerModeScreen parse both nostrconnect:// and bunker://
  (Amber presents bunker://; signer pubkey extracted before '@')
- Signer permission surface made async (permissions, can_*, is_connection_valid)
- tests/nip46_e2e.rs: full client handshake against fake Amber over a local
  relay — NIP-44 round-trip, get_public_key identity, signed-event verification,
  vault persistence asserting no secret material for remote profiles
- prettier formatting of touched frontend files

Cargo.toml

@@ -20,3 +20,10 @@ rpassword = "7"
 sha2 = "0.10"
 async-trait = "0.1"
 keyring = "4.2"
+
+[dev-dependencies]
+base64 = "0.22"
+futures-util = "0.3"
+getrandom = "0.2"
+nostr = "0.45"
+tokio-tungstenite = "0.28"