fix(network-proxy): add unix socket allow-all and update seatbelt rules (#11368)

## Summary
Adds support for a Unix socket escape hatch so we can bypass socket
allowlisting when explicitly enabled.

## Description
* added a new flag, `network.dangerously_allow_all_unix_sockets` as an
explicit escape hatch
* In codex-network-proxy, enabling that flag now allows any absolute
Unix socket path from x-unix-socket instead of requiring each path to be
explicitly allowlisted. Relative paths are still rejected.
* updated the macOS seatbelt path in core so it enforces the same Unix
socket behavior:
  * allowlisted sockets generate explicit network* subpath rules
  * allow-all generates a broad network* (subpath "/") rule

---------

Co-authored-by: Codex <199175422+chatgpt-codex-connector[bot]@users.noreply.github.com>

codex-rs/network-proxy/src/http_proxy.rs

@@ -378,8 +378,8 @@ async fn http_plain_proxy(
     };
 
     // `x-unix-socket` is an escape hatch for talking to local daemons. We keep it tightly scoped:
-    // macOS-only + explicit allowlist, to avoid turning the proxy into a general local capability
-    // escalation mechanism.
+    // macOS-only + explicit allowlist by default, to avoid turning the proxy into a general local
+    // capability escalation mechanism.
     if let Some(unix_socket_header) = req.headers().get("x-unix-socket") {
         let socket_path = match unix_socket_header.to_str() {
             Ok(value) => value.to_string(),