fix(wallet): Minibits default Cashu mint, resilient peer-file invoices, named default federation

- Cashu default mint was the local Fedimint guardian (:8175), wrongly surfacing
  a Fedimint URL in the Cashu mints list. Default is now Minibits
  (https://mint.minibits.cash/Bitcoin) — Cashu and Fedimint are distinct
  protocols (Fedimint lives under its own tab).
- Peer-file (buy) invoice creation: retry the LND REST call (3× / 400ms) so a
  transient LND-REST blip (swap pressure / just-restarted / TLS race) no longer
  hard-fails as an opaque 503, and surface the real error chain ({:#}) in the
  response + logs instead of a generic "Failed to create invoice".
- Autojoined default federation now shows a friendly name ("Archipelago
  Federation") in the Fedimint tab instead of a bare federation id.

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

core/archipelago/src/api/handler/content.rs

@@ -222,8 +222,12 @@ impl ApiHandler {
                 hyper::Body::from(r#"{"error":"Invoice missing payment hash"}"#),
             )),
             Err(e) => {
+                // Surface the FULL error chain ({:#}) — the generic top-level
+                // message hid the real cause (e.g. the LND REST connection
+                // failing), which made this 503 undiagnosable.
+                tracing::warn!("content invoice creation failed: {e:#}");
                 let body = serde_json::json!({
-                    "error": format!("Could not create invoice: {e}")
+                    "error": format!("Could not create invoice: {e:#}")
                 });
                 Ok(build_response(
                     StatusCode::SERVICE_UNAVAILABLE,

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

@@ -173,13 +173,42 @@ impl RpcHandler {
             "value": amount_sats.to_string(),
             "memo": memo,
         });
-        let resp = client
-            .post(format!("{LND_REST_BASE_URL}/v1/invoices"))
-            .header("Grpc-Metadata-macaroon", &macaroon_hex)
-            .json(&invoice_body)
-            .send()
-            .await
-            .context("Failed to create invoice")?;
+        // LND's REST endpoint can briefly drop/reset connections under load
+        // (swap pressure, just-restarted, TLS handshake races), which used to
+        // hard-fail the buy-file invoice with an opaque 503. Retry the send a
+        // few times with short backoff so a transient blip doesn't surface as
+        // a payment failure. The surrounding error now carries the real cause.
+        let mut last_err: Option<anyhow::Error> = None;
+        let mut resp = None;
+        for attempt in 0..3u32 {
+            match client
+                .post(format!("{LND_REST_BASE_URL}/v1/invoices"))
+                .header("Grpc-Metadata-macaroon", &macaroon_hex)
+                .json(&invoice_body)
+                .send()
+                .await
+            {
+                Ok(r) => {
+                    resp = Some(r);
+                    break;
+                }
+                Err(e) => {
+                    last_err = Some(anyhow::anyhow!(
+                        "LND REST connect failed (attempt {}): {e}",
+                        attempt + 1
+                    ));
+                    tokio::time::sleep(std::time::Duration::from_millis(400)).await;
+                }
+            }
+        }
+        let resp = match resp {
+            Some(r) => r,
+            None => {
+                return Err(last_err.unwrap_or_else(|| {
+                    anyhow::anyhow!("Failed to reach LND REST to create invoice")
+                }))
+            }
+        };
 
         let status = resp.status();
         let body: serde_json::Value = resp