fix: log Gitea transport failure causes

app/src/core/contracts.ts

@@ -123,7 +123,13 @@ export function statusMarker(issue: number, mode: Mode): Marker {
 }
 
 export function formatError(error: unknown): string {
-    if (error instanceof Error) return error.message;
+    if (error instanceof Error) {
+        if (error.cause === undefined) return error.message;
+        const cause = formatError(error.cause);
+        return cause && cause !== error.message
+            ? `${error.message}: ${cause}`
+            : error.message;
+    }
     return String(error);
 }