feat(network-proxy): structured policy signaling and attempt correlation to core (#11662)

## Summary
When network requests were blocked, downstream code often had to infer
ask vs deny from free-form response text. That was brittle and led to
incorrect approval behavior.
This PR fixes the proxy side so blocked decisions are structured and
request metadata survives reliably.

## Description
- Blocked proxy responses now carry consistent structured policy
decision data.
- Request attempt metadata is preserved across proxy env paths
(including ALL_PROXY flows).
- Header stripping was tightened so we still remove unsafe forwarding
headers, but keep metadata needed for policy handling.
- Block messages were clarified (for example, allowlist miss vs explicit
deny).
- Added unified violation log entries so policy failures can be
inspected in one place.
- Added/updated tests for these behaviors.

---------

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

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

@@ -3,6 +3,7 @@
 mod admin;
 mod config;
 mod http_proxy;
+mod metadata;
 mod network_policy;
 mod policy;
 mod proxy;
@@ -32,6 +33,7 @@ pub use proxy::NetworkProxyHandle;
 pub use proxy::PROXY_URL_ENV_KEYS;
 pub use proxy::has_proxy_url_env_vars;
 pub use proxy::proxy_url_env_value;
+pub use runtime::BlockedRequest;
 pub use runtime::ConfigReloader;
 pub use runtime::ConfigState;
 pub use runtime::NetworkProxyState;