test(good-fences): the model counts the rs in strawberry (red)

A first integration test of the model call: Workers AI through the AI
binding, behind the same `complete(messages)` interface as the sim's
fake model. Opt-in (`pnpm test:model`) since it needs `wrangler login`
and costs money.

Red: src/model.ts doesn't exist yet.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

good-fences/vitest.model.config.ts

@@ -0,0 +1,8 @@
+import { defineProject } from "vitest/config";
+import { cloudflareTest } from "@cloudflare/vitest-plugin";
+
+/** opt-in (`pnpm test:model`): calls Workers AI, which needs `wrangler login` and costs money */
+export default defineProject({
+	plugins: [cloudflareTest({ wrangler: { configPath: "./wrangler.model-tests.jsonc" } })],
+	test: { include: ["itest/**/*.test.ts"] },
+});