fix(cli): support legacy use_linux_sandbox_bwrap flag (#14473)

## Summary
- restore `use_linux_sandbox_bwrap` as a removed feature key so older
`--enable` callers parse again
- keep it as a no-op by leaving runtime behavior unchanged
- add regression coverage for the legacy `--enable` path

## Testing
- Not run (updated and pushed quickly)

codex-rs/core/src/features.rs

@@ -108,6 +108,9 @@ pub enum Feature {
     WebSearchCached,
     /// Legacy search-tool feature flag kept for backward compatibility.
     SearchTool,
+    /// Removed legacy Linux bubblewrap opt-in flag retained as a no-op so old
+    /// wrappers and config can still parse it.
+    UseLinuxSandboxBwrap,
     /// Use the legacy Landlock Linux sandbox fallback instead of the default
     /// bubblewrap pipeline.
     UseLegacyLandlock,
@@ -640,6 +643,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::UseLinuxSandboxBwrap,
+        key: "use_linux_sandbox_bwrap",
+        stage: Stage::Removed,
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::UseLegacyLandlock,
         key: "use_legacy_landlock",