fix(test): bump model-smoke timeout 60s → 120s (#764)

xai/grok-4.3 jobs in the models-live matrix land at 42-67s wall time vs
23-41s for every other provider, brushing the 60s ceiling and crossing
it intermittently (e.g. xai/grok-code-fast in run 25949844470 timed out
at 60s with `OK` already in stdout — model replied, harness just hadn't
seen close). 120s gives ~2x headroom on the slowest provider without
penalizing the fast-path providers, since the timer only fires on
actual hangs.

test/model-smoke.ts

@@ -28,7 +28,12 @@ config({ path: join(import.meta.dirname, "..", "..", ".env") });
 
 const PROMPT = "Reply with exactly OK and nothing else.";
 const MATCH = /\bOK\b/i;
-const TIMEOUT_MS = 60_000;
+// xai is the slowest provider in the matrix — winning xai/grok-4.3 jobs land
+// at 42-67s wall time (vs 23-41s for every other provider), brushing a 60s
+// ceiling and intermittently crossing it. 120s gives ~2x headroom on the
+// slowest provider observed in CI, with no downside on the fast-path
+// providers since the timer only fires on actual hangs.
+const TIMEOUT_MS = 120_000;
 
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