Fix deployment issues and bring in line with latest SDK

[aron-cf]

Deploying the starter on Wrangler 4.113 or newer fails with The "legacy_env" field is no longer supported. The pinned @cloudflare/vite-plugin@1.42.3 writes "legacy_env": true into the generated dist/*/wrangler.json, a field Wrangler has since removed.

Upgrading agents, @cloudflare/ai-chat, @cloudflare/vite-plugin and wrangler to their current releases fixes this, since the newer plugin no longer emits the field.

The upgrade also drops the direct @cloudflare/workers-types dependency in favor of types generated by wrangler types, avoiding a peer conflict between Wrangler (wants version 5) and partyserver (wants version 4); the generated env.d.ts is committed so a fresh clone type-checks without a build.

The same change realigns the template with the reference chat example in cloudflare/agents:

• The agent moves to the current kimi-k2.7-code model, waits for tool servers to reconnect after hibernation, prunes old reasoning, and allows more steps per turn.
• The client walks message parts in a single ordered pass, so text, reasoning and tool calls render in the order they happened, which also clears a React duplicate-key warning.
• Failed tool calls show their error instead of nothing, and tool inputs are shown while running and after.
• Minor cleanups: the compatibility date moves to the current standard, an invalid data-theme="workers" attribute is removed, and the README documents that npm run dev needs a Cloudflare login because Workers AI has no local simulator.