Bump deps; remove decorators; use agents tsconfig

Update package.json dependency versions (bump @cloudflare/ai-chat, agents, ai, workers-ai-provider) and add @types/node as a devDependency. Remove src/decorators.ts (the Babel-based decorator workaround). Simplify tsconfig.json to extend agents/tsconfig (remove local compilerOptions; leave space for overrides). Minor change to vite.config.ts imports.

Author: threepointone