[BUG]: Skill popup blocks $ env vars when no matches

What version of Codex is running?

Built from source @ 05b9606 (codex-rs)

What subscription do you have?

ChatGPT Plus

Which model were you using?

N/A

What platform is your computer?

Darwin 25.2.0 arm64 arm

What terminal emulator and version are you using (if applicable)?

Ghostty + tmux

What issue are you seeing?

In the TUI composer, any $token triggers the skill popup even when no skills match. Typing echo $HOME (or just $HOME) shows a "no skills" popup and Enter does not submit the message. This makes it impossible to send common shell snippets like echo $HOME.

Additionally, if a file popup was open (via @), switching to a $token with no matches can leave the file popup visible.

What steps can reproduce the bug?

1. Ensure at least one skill is configured.
2. In the composer, type echo $HOME (or $HOME).
3. Press Enter.
4. Observe that the message does not submit and the "no skills" popup is shown.

Optional:

1. Type @README.md to open file popup.
2. Replace text with $HOME.
3. Observe file popup can remain visible with no @ token.

What is the expected behavior?

Only open the skill popup for an empty $ or a query that matches at least one skill; otherwise, allow normal submission and clear unrelated popups.

Additional information

Fix prepared on branch fix/skill-popup-gate (tui + tui2).