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/wrangler.model-tests.jsonc

@@ -0,0 +1,7 @@
+{
+	"$schema": "node_modules/wrangler/config-schema.json",
+	// model integration tests: AI always runs remotely, and costs money
+	"name": "good-fences-model-tests",
+	"compatibility_date": "2026-10-01",
+	"ai": { "binding": "AI", "remote": true }
+}