Add MCP UI and server-side MCP integration

Add an MCP servers panel to the chat UI (src/app.tsx) with state, add/remove server actions, auth popup handling, outside-click closing, and tool summary badge. Update ChatAgent (src/server.ts) to wait for MCP connections, configure OAuth callback on start, expose callable addServer/removeServer methods, and include connected MCP tools in the server-side tools set. Update wrangler.jsonc to route /oauth/* before other workers. Bump dependencies and lockfile versions (package.json & package-lock.json) for @cloudflare/ai-chat, agents, ai, oxfmt, and related packages.

Author: threepointone