Update guardian output schema (#17061)

## Summary
- Update guardian output schema to separate risk, authorization,
outcome, and rationale.
- Feed guardian rationale into rejection messages.
- Split the guardian policy into template and tenant-config sections.

## Validation
- `cargo test -p codex-core mcp_tool_call`
- `env -u CODEX_SANDBOX_NETWORK_DISABLED INSTA_UPDATE=always cargo test
-p codex-core guardian::`

---------

Co-authored-by: Owen Lin <owen@openai.com>

codex-rs/core/src/state/service.rs

@@ -1,3 +1,4 @@
+use std::collections::HashMap;
 use std::sync::Arc;
 
 use crate::RolloutRecorder;
@@ -46,6 +47,7 @@ pub(crate) struct SessionServices {
     pub(crate) models_manager: Arc<ModelsManager>,
     pub(crate) session_telemetry: SessionTelemetry,
     pub(crate) tool_approvals: Mutex<ApprovalStore>,
+    pub(crate) guardian_rejection_rationales: Mutex<HashMap<String, String>>,
     pub(crate) skills_manager: Arc<SkillsManager>,
     pub(crate) plugins_manager: Arc<PluginsManager>,
     pub(crate) mcp_manager: Arc<McpManager>,