fix(test): widen capturedHandler cast to resolve TS2349 never narrowing (FAR-40)

TypeScript CFA does not trace the assignment inside the vi.spyOn
mockImplementation callback, so it narrows capturedHandler to null at
the if-check, making the body unreachable (never). Cast at the call
site breaks the false narrowing without changing runtime behaviour.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/server/execute.test.ts

@@ -357,7 +357,7 @@ describe("execute — SIGTERM handler", () => {
     if (capturedHandler) {
       const batchApi = vi.mocked(getBatchApi)();
       // Fire the handler and verify it deletes the job that was just created.
-      try { capturedHandler(); } catch { /* swallow process.exit throw */ }
+      try { (capturedHandler as () => void)(); } catch { /* swallow process.exit throw */ }
       await new Promise((r) => setTimeout(r, 50)); // let async handler tick
       expect(batchApi.deleteNamespacedJob).toHaveBeenCalled();
     }