feat(wallet): pay for peer files from BOTH Cashu and Fedimint ecash (#3)

Paying for a peer file minted a Cashu-only token, so a node whose ecash balance
lived in Fedimint couldn't pay even with funds. Now both backends are tried:

- payer (content.download-peer-paid): mint a Cashu token first; on failure fall
  back to spending Fedimint notes. Only error if BOTH backends can't cover it.
- seller (verify_and_receive_payment): accept Fedimint notes as well as Cashu —
  anything not starting with "cashu" is redeemed via reissue_into_any.
- new fedimint_client::spend_from_any() — spend from whichever joined federation
  has the balance, returning the notes + federation id (mirrors reissue_into_any).
- wallet.ecash-balance now also reports fedimint_sats + combined total_sats; the
  pay-for-file pre-check uses the combined total so a Fedimint-funded node isn't
  wrongly blocked.

Compiles (cargo check + vue-tsc). Live cross-node federation validation pending
(dual-ecash phase 6) — needs two nodes sharing a federation.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

core/archipelago/src/wallet/ecash.rs

@@ -1118,6 +1118,24 @@ pub async fn verify_and_receive_payment(
         return Ok(received);
     }
 
+    // Fedimint notes (#3): a buyer whose balance is in Fedimint pays with notes
+    // rather than a Cashu token. Cashu tokens all start with "cashu" (cashuA/
+    // cashuB, or the legacy form handled above), so anything else is treated as
+    // Fedimint notes and redeemed into a joined federation. reissue_into_any
+    // verifies the notes are unspent and credits this node's wallet.
+    if !token_str.starts_with("cashu") {
+        let (received, _fed_id) =
+            crate::wallet::fedimint_client::reissue_into_any(data_dir, token_str).await?;
+        if received < required_sats {
+            anyhow::bail!(
+                "Insufficient payment: {} sats, need {} sats",
+                received,
+                required_sats
+            );
+        }
+        return Ok(received);
+    }
+
     // Parse and validate cashuA token
     let token = CashuToken::deserialize(token_str)?;
     let total = token.total_amount();