add per-agent smoke tests (#100)

test/fixtures/smoke.ts

@@ -0,0 +1,12 @@
+import type { Inputs } from "../../main.ts";
+
+/**
+ * smoke test fixture - minimal prompt to verify:
+ * 1. agent connects to API
+ * 2. MCP server responds
+ * 3. select_mode tool works
+ */
+export default {
+  prompt: `Call the select_mode tool with modeName "Build" and confirm you received the mode's prompt instructions. Then say "SMOKE TEST PASSED".`,
+  effort: "mini",
+} satisfies Inputs;