feat: add AgentsKit Workers AI agent template

[EmersonBraun]

What changed

• add a self-contained AgentsKit agent template backed by the native Workers AI binding
• translate Workers AI events into provider-neutral AgentsKit text, error, and done stream chunks
• expose a validated SSE chat API and a responsive browser interface
• add 11 request and adapter tests plus a Playwright smoke test
• register the template with Cloudflare metadata and reproducible npm and pnpm lockfiles

Why

This gives Cloudflare developers a small, edge-native starting point for composing an agent around Workers AI without an external provider key. The adapter boundary keeps the inference stream compatible with AgentsKit's message and streaming contracts, so users can add memory, tools, retrieval, or another provider without replacing the UI and API flow.

Validation

• pnpm --filter agentskit-agent-template test — 11 tests passed
• pnpm --filter agentskit-agent-template check — TypeScript and Wrangler dry-run passed
• pnpm exec playwright test playwright-tests/agentskit-agent-template.spec.ts --reporter=list — Chromium smoke test passed
• pnpm run check — 72 repository tasks passed, including template lint, lockfile validation, builds, type generation, dry-runs, and Prettier

The dry-run bundles the Worker at 40.30 KiB (8.93 KiB gzip) with only the native AI and ASSETS bindings. No credentials or external API keys are included.

[EmersonBraun]

Hi — would this Workers AI template still be a fit for the catalog? The branch is mergeable and the template was rebased and revalidated against current main. I'm happy to adjust its metadata or structure to current conventions.