fix: surface cocod "Not enough proofs" as InsufficientBalanceError

When cocod cannot assemble enough proofs to send (e.g. due to
denomination fragmentation or stale proof state), it returns
"Send failed: Not enough proofs to send". This was propagating
as a generic Error, causing the HTTP handler to return 500 instead
of the structured 402 insufficient_balance response.

Map that cocod error to InsufficientBalanceError in walletAdapter.sendToken
so the existing handler path returns the correct 402.

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

src/daemon/wallet/index.ts

@@ -1,4 +1,5 @@
 import { getDecodedToken } from "@cashu/cashu-ts";
+import { InsufficientBalanceError } from "@routstr/sdk";
 import { logger } from "../../utils/logger";
 import { createCocodClient, type CocodClient } from "./cocod-client";
 
@@ -79,6 +80,10 @@ export async function createWalletAdapter(
             continue;
           }
 
+          if (errorMessage.includes("Not enough proofs")) {
+            throw new InsufficientBalanceError(amount, 0);
+          }
+
           logger.error("Error in walletAdapter sendToken:", error);
           throw error;
         }