Route exec-server HTTP through configured proxy policy (#35023)

## Why

Delegated HTTP requests need to honor the same outbound proxy policy as the
Codex process that starts the exec server.

## What changed

- Pass the configured `HttpClientFactory` through local and remote exec-server
  startup and use route-aware client pools for delegated HTTP and local MCP
  requests.
- Preserve per-request timeouts and follow-or-stop redirect behavior while
  keeping request URLs and sensitive response headers out of diagnostics.

## Testing

- Cover configured system-proxy routing across the exec-server transport.
- Cover both redirect policies and verify that success and failure logs do not
  expose request or response secrets.

GitOrigin-RevId: 4af6aec1d265c4db62dfcb6e1fb076fb31736137

codex-rs/rmcp-client/Cargo.toml

@@ -18,6 +18,7 @@ base64 = { workspace = true }
 codex-api = { workspace = true }
 codex-config = { workspace = true }
 codex-exec-server = { workspace = true }
+codex-http-client = { workspace = true }
 codex-keyring-store = { workspace = true }
 codex-protocol = { workspace = true }
 codex-secrets = { workspace = true }