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.

core/archipelago/src/api/rpc/wallet.rs

@@ -421,6 +421,25 @@ impl RpcHandler {
         }))
     }
 
+    /// `wallet.ecash-lnaddress` — the node's Minibits Lightning address
+    /// (`<name>@minibits.cash`, LUD-16), derived from and authenticated by the
+    /// ecash wallet's own seed. Registers the profile on first use; safe to call
+    /// on every open of the Cashu receive screen (it is idempotent).
+    pub(super) async fn handle_wallet_ecash_lnaddress(&self) -> Result<serde_json::Value> {
+        crate::wallet::minibits::lnaddress(&self.config.data_dir).await
+    }
+
+    /// `wallet.ecash-lnaddress-claim` — redeem any Lightning payments that
+    /// arrived on the node's Minibits address as ecash. Returns the sats swept in
+    /// (0 when nothing was waiting), so the UI can refresh its balance.
+    pub(super) async fn handle_wallet_ecash_lnaddress_claim(&self) -> Result<serde_json::Value> {
+        let outcome = crate::wallet::minibits::claim_and_redeem(&self.config.data_dir).await?;
+        Ok(serde_json::json!({
+            "claimed_count": outcome.claimed_count,
+            "received_sats": outcome.received_sats,
+        }))
+    }
+
     pub(super) async fn handle_wallet_networking_profits(&self) -> Result<serde_json::Value> {
         let summary = profits::get_networking_profits(&self.config.data_dir).await?;
         Ok(serde_json::json!({