Honor system proxy settings in the daemon updater (#34495)

## Why

The PID-managed daemon updater downloaded the standalone installer directly,
bypassing Codex's configured outbound proxy policy.

## What changed

- Build the updater's HTTP client from the effective Codex configuration so
  `features.respect_system_proxy` also applies to installer downloads.
- Use the route-aware client pool for the installer request.
- Warn and fall back to the default `reqwest` proxy behavior when configuration
  cannot be loaded, allowing updates to continue.

## Testing

Added tests for proxy-policy selection, configuration-load fallback, exact
installer URL usage, byte preservation, and non-success HTTP responses.

GitOrigin-RevId: 559668eb40314d43afa6512da66e59e32cc1b93c

codex-rs/Cargo.lock

@@ -2075,12 +2075,12 @@ dependencies = [
  "anyhow",
  "codex-app-server-protocol",
  "codex-app-server-transport",
+ "codex-http-client",
  "codex-uds",
  "codex-utils-home-dir",
  "futures",
  "libc",
  "pretty_assertions",
- "reqwest 0.12.28",
  "serde",
  "serde_json",
  "sha2 0.10.9",
@@ -2331,6 +2331,7 @@ dependencies = [
  "codex-features",
  "codex-git-utils",
  "codex-home",
+ "codex-http-client",
  "codex-install-context",
  "codex-login",
  "codex-mcp",