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/codex_delegate_tests.rs

@@ -317,8 +317,8 @@ async fn handle_exec_approval_uses_call_id_for_guardian_review_and_approval_id_f
             id: "command-item-1".to_string(),
             turn_id: parent_ctx.sub_id.clone(),
             status: GuardianAssessmentStatus::InProgress,
-            risk_score: None,
             risk_level: None,
+            user_authorization: None,
             rationale: None,
             action: GuardianAssessmentAction::Command {
                 source: GuardianCommandSource::Shell,