tui: retire /approvals and rename /autoreview to /approve (#21034)

## Why

The TUI currently exposes overlapping command names for the same
permissions flow: `/permissions` and the older `/approvals` alias. It
also uses `/autoreview` for the manual retry flow, even though the
action users take there is approving one denied auto-review request.

This change makes the command surface consistent with the hard rebrand:
- `/permissions` is the only command for permission settings.
- `/approve` is the command for approving a recent auto-review denial.

## What changed

- Removed the legacy `/approvals` slash command and its dispatch path.
- Kept `/permissions` as the single permissions command shown and
accepted by the TUI.
- Renamed the auto-review denial command from `/autoreview` to
`/approve`.
- Updated nearby comments so they refer to `/permissions` rather than
the retired `/approvals` name.

## Verification

- Updated the slash-command unit test to assert that `AutoReview` now
renders and parses as `approve`.

codex-rs/tui/src/app/config_persistence.rs

@@ -203,7 +203,7 @@ impl App {
                 let previous_approvals_reviewer = feature_config.approvals_reviewer;
                 if effective_enabled {
                     // Persist the reviewer setting so future sessions keep the
-                    // experiment's matching `/approvals` mode until the user
+                    // experiment's matching `/permissions` mode until the user
                     // changes it explicitly.
                     feature_config.approvals_reviewer = auto_review_preset.approvals_reviewer;
                     feature_edits.push(ConfigEdit::SetPath {
@@ -323,7 +323,7 @@ impl App {
                 .await;
             // This uses `OverrideTurnContext` intentionally: toggling the
             // experiment should update the active thread's effective approval
-            // settings immediately, just like a `/approvals` selection. Without
+            // settings immediately, just like a `/permissions` selection. Without
             // this runtime patch, the config edit would only affect future
             // sessions or turns recreated from disk.
             let op = AppCommand::override_turn_context(