feat: load the local Cloudflare bindings automatically

[yusukebe]

In a project with a wrangler config, c.env now carries the real local bindings (KV, D1, R2, vars) in request, batch, and snapshot — wrangler's getPlatformProxy simulates the binding backends while the app stays on Node.js. Automatic on purpose: a flag nobody routes to does not exist, and the correct default needs no rail. --no-bindings skips it; a missing wrangler warns and continues; a broken config fails as BINDINGS_FAILED. wrangler stays out of the dependencies (resolved from the project, like the workerd path).

Verified against a real Workers project: vars and KV reach c.env, a KV put→get flow passes in one batch --compact call, the proxy disposes cleanly (no hang), and non-wrangler projects are untouched. Logged in docs/agent-dx-log.md; agent-dx measures next with a D1/KV fixture.

The author should do the following, if applicable

• Add tests
• Run tests
• pnpm run format:fix && pnpm run lint:fix to format the code
• Add TSDoc/JSDoc to document the code