fix: allow proper exit from new Switch approval mode dialog (#453)

As described in
https://github.com/openai/codex/issues/392#issuecomment-2817090022
introduced by #400

The testing I'd done worked correctly because I was using the (s)
shortcut, but selecting the same option using arrow‑key → Enter on
“Switch approval mode” was preventing the user from subsequently exiting
the Switch approval mode dialog, requiring a ^C to quit codex entirely.
With this fix, both entry methods work correctly in my testing.

Per codex:

Issue

- When you navigated down (↓) to “Switch approval mode (s)” in the Shell
Command review dialog and pressed Enter, the ApprovalModeOverlay would
open—but because the underlying `TerminalChatCommandReview` component
stayed mounted (albeit disabled), its own Ink input handlers immediately
re‑captured the same key events and re‑opened the overlay as soon as you
hit Esc or Enter again. In practice this made it impossible to exit the
submenu.

Root cause

- We only disabled the SelectInput via `isDisabled`, but never fully
unmounted the review UI when an overlay was shown, so its `useInput` and
`<Select>` hooks were still active and “stealing” keys.

Fix

- In `terminal-chat.tsx` we now only render `<TerminalChatInput>` (and
by extension `TerminalChatCommandReview`) when `overlayMode === "none"`.
That unmounts all of its key handlers whenever any overlay (history,
model, approval, help, diff) is open, so no input leaks through.

Files changed

- **src/components/chat/terminal-chat.tsx**: Wrapped the entire
`<TerminalChatInput>` block in `overlayMode === "none" && agent`

With that in place, arrow‑key → Enter on “Switch approval mode”
correctly opens the overlay, and then you can use Enter/Esc inside the
overlay without getting stuck or immediately re‑opening it.

codex-cli/src/components/chat/terminal-chat.tsx

@@ -490,7 +490,7 @@ export default function TerminalChat({
             <Text color="gray">Initializing agent…</Text>
           </Box>
         )}
-        {agent && (
+        {overlayMode === "none" && agent && (
           <TerminalChatInput
             loading={loading}
             setItems={setItems}