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/tui/src/debug_config.rs

@@ -618,7 +618,7 @@ mod tests {
             allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::GuardianSubagent]),
             allowed_sandbox_modes: Some(vec![SandboxModeRequirement::ReadOnly]),
             allowed_web_search_modes: Some(vec![WebSearchModeRequirement::Cached]),
-            guardian_developer_instructions: None,
+            guardian_policy_config: None,
             feature_requirements: Some(FeatureRequirementsToml {
                 entries: BTreeMap::from([("guardian_approval".to_string(), true)]),
             }),
@@ -811,7 +811,7 @@ approval_policy = "never"
             allowed_approvals_reviewers: None,
             allowed_sandbox_modes: None,
             allowed_web_search_modes: Some(Vec::new()),
-            guardian_developer_instructions: None,
+            guardian_policy_config: None,
             feature_requirements: None,
             mcp_servers: None,
             apps: None,