test(sp8): add coverage for resubmitRejectedWithDownload + bundle modal flow

- inbox-api.test.ts: pin ?download=true POST contract; blob + filename +
  X-Cyclone-Serialize-Errors parsing; non-2xx error surfacing.
- Inbox.test.tsx: end-to-end multi-select → Resubmit + Download path
  verifies api call args and downloadBlob wiring.
- inbox-api.ts: drop redundant isConfigured short-circuit in download
  variant (backend has its own auth gate) and switch error reading to
  res.text() to match Blob response shape.

src/lib/inbox-api.ts

@@ -142,7 +142,6 @@ export async function resubmitRejected(
 export async function resubmitRejectedWithDownload(
   claimIds: string[],
 ): Promise<{ blob: Blob; filename: string; serializeErrors: Array<{ claim_id: string; reason: string }> }> {
-  if (!isConfigured) throw notConfiguredError();
   const res = await fetch(
     joinUrl("/api/inbox/rejected/resubmit?download=true"),
     {
@@ -152,7 +151,7 @@ export async function resubmitRejectedWithDownload(
     },
   );
   if (!res.ok) {
-    const detail = await readErrorBody(res);
+    const detail = await res.text().catch(() => "");
     throw new Error(
       `${res.status} ${res.statusText}${detail ? ` — ${detail}` : ""}`,
     );