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/slash_command.rs

@@ -15,7 +15,6 @@ pub enum SlashCommand {
     Model,
     Fast,
     Ide,
-    Approvals,
     Permissions,
     Keymap,
     Vim,
@@ -24,7 +23,7 @@ pub enum SlashCommand {
     #[strum(serialize = "sandbox-add-read-dir")]
     SandboxReadRoot,
     Experimental,
-    #[strum(to_string = "autoreview")]
+    #[strum(to_string = "approve")]
     AutoReview,
     Memories,
     Skills,
@@ -117,7 +116,6 @@ impl SlashCommand {
             SlashCommand::Collab => "change collaboration mode (experimental)",
             SlashCommand::Agent | SlashCommand::MultiAgents => "switch the active agent thread",
             SlashCommand::Side => "start a side conversation in an ephemeral fork",
-            SlashCommand::Approvals => "choose what Codex is allowed to do",
             SlashCommand::Permissions => "choose what Codex is allowed to do",
             SlashCommand::Keymap => "remap TUI shortcuts",
             SlashCommand::Vim => "toggle Vim mode for the composer",
@@ -184,7 +182,6 @@ impl SlashCommand {
             | SlashCommand::Model
             | SlashCommand::Fast
             | SlashCommand::Personality
-            | SlashCommand::Approvals
             | SlashCommand::Permissions
             | SlashCommand::Keymap
             | SlashCommand::Vim
@@ -274,10 +271,10 @@ mod tests {
     }
 
     #[test]
-    fn auto_review_command_is_autoreview() {
-        assert_eq!(SlashCommand::AutoReview.command(), "autoreview");
+    fn auto_review_command_is_approve() {
+        assert_eq!(SlashCommand::AutoReview.command(), "approve");
         assert_eq!(
-            SlashCommand::from_str("autoreview"),
+            SlashCommand::from_str("approve"),
             Ok(SlashCommand::AutoReview)
         );
     }