feat: implement PSBT fallback in wallet transactions

Add fallback mechanism for PSBT transactions in the SDK. When PSBT
is requested but fails, automatically retry with legacy transaction
format and record the error details for reporting.

Co-authored-by: llm-git <llm-git@ttll.de>

Ticket: BTC-2894

TICKET: BTC-2894

Author: lcovar

modules/sdk-api/src/v1/wallet.ts

@@ -914,8 +914,33 @@ Wallet.prototype.createTransaction = function (params, callback) {
   params.wallet = this;
 
   // Apply PSBT rollout logic (respects explicit usePsbt if set)
-  params.usePsbt = shouldUsePsbt(this.bitgo, params.usePsbt);
+  const wantsPsbt = shouldUsePsbt(this.bitgo, params.usePsbt);
+
+  if (wantsPsbt) {
+    // Try PSBT first, fall back to legacy on failure
+    return TransactionBuilder.createTransaction({ ...params, usePsbt: true })
+      .then((result: any) => {
+        result.psbtAttempt = { success: true };
+        return result;
+      })
+      .catch((psbtError: Error) => {
+        // PSBT failed - fall back to legacy and capture error for backend reporting
+        console.warn('PSBT transaction failed, falling back to legacy:', psbtError.message);
+        return TransactionBuilder.createTransaction({ ...params, usePsbt: false }).then((result: any) => {
+          result.psbtAttempt = {
+            success: false,
+            error: psbtError.message,
+            stack: psbtError.stack?.split('\n').slice(0, 5).join('\n'), // First 5 lines
+          };
+          return result;
+        });
+      })
+      .then(callback)
+      .catch(callback);
+  }
 
+  // Legacy path
+  params.usePsbt = false;
   return TransactionBuilder.createTransaction(params).then(callback).catch(callback);
 };
 
@@ -1746,6 +1771,7 @@ Wallet.prototype.createAndSignTransaction = function (params, callback) {
       travelInfos,
       estimatedSize,
       unspents,
+      psbtAttempt: transaction.psbtAttempt, // Propagate PSBT attempt info for error reporting
     });
   }
     .call(this)