feat: support customization of the OAuth callback path

[kherock]

This implements #75 with a new --callback-path CLI option to customize the OAuth callback endpoint.

There was already some support for customizing the callback in the NodeOAuthClientProvider and enabling this was mainly just a mattter of parsing the option from the CLI arguments.

[devmaha]

We recently forked mcp-remote and fixed a number of auth-related problems. If it's helpful, you can try the fork here: https://github.com/abluva/mcp-remote

We'll be maintaining it going forward, so feel free to open issues or PRs there if you run into anything else.

Newly released version 2.0.0 supports MCP 2026-07-28 stateless remote transport; stdio bridge (initialize shim, _meta strip, list-method shims); --protocol CLI; localhost OAuth skip; SDK 1.30