feat(ecash): Minibits @minibits.cash Lightning address on Cashu receive

The wallet used Minibits only as a Cashu mint, so the node could hold and
swap ecash there but had no addressable name at it. This derives a LUD-16
Lightning address (name@minibits.cash) from the node's own ecash wallet and
surfaces it in the ecash Receive tab above the existing paste-token box.

Identity reuses the NUT-13 ecash phrase, so there is no second secret:
  - seedHash = sha256(mnemonic.to_seed("")) — the exact hash the Minibits app
    stores, so restoring the same phrase recovers the same address both ways;
  - Nostr keys via NIP-06 at m/44'/1237'/0'/0/0 (nostr-sdk Keys::from_mnemonic,
    pinned by a unit test against the NIP-06 vector so a bump cannot silently
    move the derivation and orphan the profile).

Backend (wallet/minibits.rs) implements the verified live /v3 flow: NIP-42
challenge/verify -> JWT, idempotent /profile registration with collision
retry, and /claim polling that NIP-04-decrypts each token (service pubkey read
from the address's own LUD-16 metadata, constant fallback) and redeems it
through ecash::receive_token. Mainnet-only; state cached 0600 in
wallet/minibits.json.

New RPC: wallet.ecash-lnaddress (register-or-read, idempotent) and
wallet.ecash-lnaddress-claim (sweep Lightning payments into ecash). The modal
fetches the address on tab open, renders QR + copy, and sweeps claims while
open; a registration failure is non-fatal so paste-token still works.

Verified end-to-end against production: registered a disposable
@minibits.cash address, confirmed it resolves via /.well-known/lnurlp, and the
claim poll returns cleanly.

neode-ui/src/locales/es.json

@@ -756,6 +756,12 @@
     "paymentConfirmed": "Pago confirmado",
     "transactionId": "ID de transacci\u00f3n",
     "pasteEcashToken": "Pegar token Ecash",
+    "lnAddressTitle": "O comparte tu direcci\u00f3n Lightning de Minibits",
+    "lnAddressHint": "Cualquier persona puede pagarte sats con cualquier billetera Lightning enviando a esta direcci\u00f3n \u2014 los sats llegan como ecash. Mant\u00e9n esta pantalla abierta para recibirlos.",
+    "lnAddressLabel": "Su direcci\u00f3n @minibits.cash:",
+    "lnAddressLoading": "Configurando su direcci\u00f3n Lightning\u2026",
+    "lnAddressUnavailable": "Direcci\u00f3n Lightning no disponible \u2014 a\u00fan puede pegar un token abajo.",
+    "lnAddressReceived": "\u00a1Recibi\u00f3 {amount} sats en su direcci\u00f3n Lightning!",
     "processing": "Procesando...",
     "generateAddress": "Generar direcci\u00f3n",
     "createInvoice": "Crear factura",