feat(tui) /permissions flow (#9561)

## Summary
Adds the `/permissions` command, with a (usually) shorter set of
permissions. `/approvals` still exists, for backwards compatibility.

<img width="863" height="309" alt="Screenshot 2026-01-20 at 4 12 51 PM"
src="https://github.com/user-attachments/assets/c49b5ba5-bc47-46dd-9067-e1a5670328fe"
/>


## Testing
- [x] updated unit tests
- [x] Tested locally

codex-rs/tui/src/slash_command.rs

@@ -14,6 +14,7 @@ pub enum SlashCommand {
     // more frequently used commands should be listed first.
     Model,
     Approvals,
+    Permissions,
     #[strum(serialize = "setup-elevated-sandbox")]
     ElevateSandbox,
     Experimental,
@@ -60,6 +61,7 @@ impl SlashCommand {
             SlashCommand::Model => "choose what model and reasoning effort to use",
             SlashCommand::Collab => "change collaboration mode (experimental)",
             SlashCommand::Approvals => "choose what Codex can do without approval",
+            SlashCommand::Permissions => "choose what Codex is allowed to do",
             SlashCommand::ElevateSandbox => "set up elevated agent sandbox",
             SlashCommand::Experimental => "toggle beta features",
             SlashCommand::Mcp => "list configured MCP tools",
@@ -86,6 +88,7 @@ impl SlashCommand {
             // | SlashCommand::Undo
             | SlashCommand::Model
             | SlashCommand::Approvals
+            | SlashCommand::Permissions
             | SlashCommand::ElevateSandbox
             | SlashCommand::Experimental
             | SlashCommand::Review