feat(core): add structured network approval plumbing and policy decision model (#11672)

### Description
#### Summary
Introduces the core plumbing required for structured network approvals

#### What changed
- Added structured network policy decision modeling in core.
- Added approval payload/context types needed for network approval
semantics.
- Wired shell/unified-exec runtime plumbing to consume structured
decisions.
- Updated related core error/event surfaces for structured handling.
- Updated protocol plumbing used by core approval flow.
- Included small CLI debug sandbox compatibility updates needed by this
layer.

#### Why
establishes the minimal backend foundation for network approvals without
yet changing high-level orchestration or TUI behavior.

#### Notes
- Behavior remains constrained by existing requirements/config gating.
- Follow-up PRs in the stack handle orchestration, UX, and app-server
integration.

---------

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

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

@@ -18,7 +18,9 @@ pub use config::NetworkMode;
 pub use config::NetworkProxyConfig;
 pub use config::host_and_port_from_network_addr;
 pub use network_policy::NetworkDecision;
+pub use network_policy::NetworkDecisionSource;
 pub use network_policy::NetworkPolicyDecider;
+pub use network_policy::NetworkPolicyDecision;
 pub use network_policy::NetworkPolicyRequest;
 pub use network_policy::NetworkPolicyRequestArgs;
 pub use network_policy::NetworkProtocol;
@@ -34,6 +36,8 @@ 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::BlockedRequestArgs;
+pub use runtime::BlockedRequestObserver;
 pub use runtime::ConfigReloader;
 pub use runtime::ConfigState;
 pub use runtime::NetworkProxyState;