fix: Avoid panic in sandboxed environments by removing system-configuration dependency (#11828)
## Summary
Fixes #11826
- Replace `hyper-util`'s `"full"` feature flag with only the features
actually used (`client-legacy`, `http1`, `http2`, `tokio`) in
`turborepo-microfrontends-proxy`
- This removes the `system-configuration` crate from the dependency tree
entirely
## Why
The `"full"` feature on `hyper-util` includes `"client-proxy-system"`,
which pulls in the
[`system-configuration`](https://crates.io/crates/system-configuration)
crate on macOS. Due to Cargo feature unification, this feature was
activated for **all** `hyper-util` consumers in the workspace, including
`reqwest`.
When `reqwest` builds a client, it calls
`SCDynamicStoreCreateWithOptions()` to detect system proxy settings. In
sandboxed environments (e.g. OpenAI Codex), this macOS API returns NULL,
and the `system-configuration` crate panics with "Attempted to create a
NULL object" — crashing turbo with exit code 101.
The microfrontends proxy never needed system proxy detection. It only
uses `hyper-util` for its HTTP client (`Client::builder`), `TokioIo`,
`TokioExecutor`, and HTTP/1+2 support.
## Testing
- `cargo check --workspace` passes
- All 13 `turborepo-microfrontends-proxy` tests pass
- `cargo tree --workspace | grep system-configuration` returns nothing —
the dependency is fully removed