Fix auto-review config compatibility across protocol and SDK (#19113)

## Why

This keeps the partial Guardian subagent -> Auto-review rename
forward-compatible across mixed Codex installations. Newer binaries need
to understand the new `auto_review` spelling, but they cannot write it
to shared `~/.codex/config.toml` yet because older CLI/app-server
bundles only know `user` and `guardian_subagent` and can fail during
config load before recovering.

The Python SDK had the opposite compatibility gap: app-server responses
can contain `approvalsReviewer: "auto_review"`, but the checked-in
generated SDK enum did not accept that value.

## What Changed

- Keep `ApprovalsReviewer::AutoReview` readable from both
`guardian_subagent` and `auto_review`, while serializing it as
`guardian_subagent` in both protocol crates.
- Update TUI Auto-review persistence tests so enabling Auto-review
writes `approvals_reviewer = "guardian_subagent"` while UI copy still
says Auto-review.
- Map managed/cloud `feature_requirements.auto_review` to the existing
`Feature::GuardianApproval` gate without adding a broad local
`[features].auto_review` key or changing config writes.
- Add `auto_review` to the Python SDK `ApprovalsReviewer` enum and cover
`ThreadResumeResponse` validation.

## Testing

- `cargo test -p codex-protocol approvals_reviewer`
- `cargo test -p codex-app-server-protocol approvals_reviewer`
- `cargo test -p codex-tui
update_feature_flags_enabling_guardian_selects_auto_review`
- `cargo test -p codex-tui
update_feature_flags_enabling_guardian_in_profile_sets_profile_auto_review_policy`
- `cargo test -p codex-core
feature_requirements_auto_review_disables_guardian_approval`
- `pytest
sdk/python/tests/test_client_rpc_methods.py::test_thread_resume_response_accepts_auto_review_reviewer`
- `git diff --check`

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -325,7 +325,7 @@ impl From<CoreAskForApproval> for AskForApproval {
 pub enum ApprovalsReviewer {
     #[serde(rename = "user")]
     User,
-    #[serde(rename = "auto_review", alias = "guardian_subagent")]
+    #[serde(rename = "guardian_subagent", alias = "auto_review")]
     AutoReview,
 }
 
@@ -7500,7 +7500,7 @@ mod tests {
         );
         assert_eq!(
             serde_json::to_string(&ApprovalsReviewer::AutoReview).expect("serialize reviewer"),
-            "\"auto_review\""
+            "\"guardian_subagent\""
         );
 
         for value in ["user", "auto_review", "guardian_subagent"] {