Rename approvals reviewer variant to auto-review (#19056)

## Why

`approvals_reviewer` now uses `auto_review` as the canonical config/API
value after #18504, but the Rust enum variant and nearby helper/test
names still used `GuardianSubagent` / guardian approval wording. That
made follow-up code and reviews confusing even though the external value
had already moved to Auto-review.

## What changed

- Renamed `ApprovalsReviewer::GuardianSubagent` to
`ApprovalsReviewer::AutoReview`.
- Updated protocol, app-server, config, core, TUI, exec, and analytics
test callsites.
- Renamed nearby helper/test names from guardian approval wording to
Auto-review wording where they refer to the approvals reviewer mode.
- Preserved wire compatibility:
  - `auto_review` remains the canonical serialized value.
  - `guardian_subagent` remains accepted as a legacy alias.

This intentionally does not rename the `[features].guardian_approval`
key, `Feature::GuardianApproval`, `core/src/guardian`, analytics event
names, or app-server Guardian review event types.

## Verification

- `cargo test -p codex-protocol
approvals_reviewer_serializes_auto_review_and_accepts_legacy_guardian_subagent`
- `cargo test -p codex-app-server-protocol
approvals_reviewer_serializes_auto_review_and_accepts_legacy_guardian_subagent`
- `cargo test -p codex-config approvals_reviewer`
- `cargo test -p codex-tui update_feature_flags`
- `cargo test -p codex-core permissions_instructions`
- `cargo test -p codex-tui permissions_selection`

codex-rs/core/src/config/config_tests.rs

@@ -6741,10 +6741,7 @@ approvals_reviewer = "guardian_subagent"
         .build()
         .await?;
 
-    assert_eq!(
-        config.approvals_reviewer,
-        ApprovalsReviewer::GuardianSubagent
-    );
+    assert_eq!(config.approvals_reviewer, ApprovalsReviewer::AutoReview);
     Ok(())
 }
 
@@ -6757,17 +6754,14 @@ async fn requirements_disallowing_default_approvals_reviewer_falls_back_to_requi
         .codex_home(codex_home.path().to_path_buf())
         .cloud_requirements(CloudRequirementsLoader::new(async {
             Ok(Some(crate::config_loader::ConfigRequirementsToml {
-                allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::GuardianSubagent]),
+                allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::AutoReview]),
                 ..Default::default()
             }))
         }))
         .build()
         .await?;
 
-    assert_eq!(
-        config.approvals_reviewer,
-        ApprovalsReviewer::GuardianSubagent
-    );
+    assert_eq!(config.approvals_reviewer, ApprovalsReviewer::AutoReview);
     Ok(())
 }
 
@@ -6786,17 +6780,14 @@ async fn root_approvals_reviewer_falls_back_when_disallowed_by_requirements() ->
         .fallback_cwd(Some(codex_home.path().to_path_buf()))
         .cloud_requirements(CloudRequirementsLoader::new(async {
             Ok(Some(crate::config_loader::ConfigRequirementsToml {
-                allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::GuardianSubagent]),
+                allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::AutoReview]),
                 ..Default::default()
             }))
         }))
         .build()
         .await?;
 
-    assert_eq!(
-        config.approvals_reviewer,
-        ApprovalsReviewer::GuardianSubagent
-    );
+    assert_eq!(config.approvals_reviewer, ApprovalsReviewer::AutoReview);
     assert!(
         config.startup_warnings.iter().any(|warning| {
             warning
@@ -6826,17 +6817,14 @@ approvals_reviewer = "user"
         .fallback_cwd(Some(codex_home.path().to_path_buf()))
         .cloud_requirements(CloudRequirementsLoader::new(async {
             Ok(Some(crate::config_loader::ConfigRequirementsToml {
-                allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::GuardianSubagent]),
+                allowed_approvals_reviewers: Some(vec![ApprovalsReviewer::AutoReview]),
                 ..Default::default()
             }))
         }))
         .build()
         .await?;
 
-    assert_eq!(
-        config.approvals_reviewer,
-        ApprovalsReviewer::GuardianSubagent
-    );
+    assert_eq!(config.approvals_reviewer, ApprovalsReviewer::AutoReview);
     Ok(())
 }
 
@@ -6857,7 +6845,7 @@ async fn approvals_reviewer_preserves_valid_user_choice_when_allowed_by_requirem
             Ok(Some(crate::config_loader::ConfigRequirementsToml {
                 allowed_approvals_reviewers: Some(vec![
                     ApprovalsReviewer::User,
-                    ApprovalsReviewer::GuardianSubagent,
+                    ApprovalsReviewer::AutoReview,
                 ]),
                 ..Default::default()
             }))
@@ -6865,10 +6853,7 @@ async fn approvals_reviewer_preserves_valid_user_choice_when_allowed_by_requirem
         .build()
         .await?;
 
-    assert_eq!(
-        config.approvals_reviewer,
-        ApprovalsReviewer::GuardianSubagent
-    );
+    assert_eq!(config.approvals_reviewer, ApprovalsReviewer::AutoReview);
     assert!(
         config
             .startup_warnings