Prompt name filtering fails for partial matches

What version of Codex is running?

0.93.0

What subscription do you have?

Plus

Which model were you using?

_No response_

What platform is your computer?

_No response_

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

_No response_

What issue are you seeing?

While using https://github.com/github/spec-kit the prompt files are named in a pattern like speckit.plan.md.
When filtering for prompts the input /speckit surfaces all of the results ok, but when the input is /plan the TUI responds with no matches, making it less convenient to navigate a collection of prompts speckit provides.

Looks like a bug, as comment on the related function suggests such approach should work
https://github.com/openai/codex/blob/2a299317d208f8d41a62b9350e4c5eeb124e60d2/codex-rs/tui/src/bottom_pane/command_popup.rs#L174

Happy to submit a PR for this

What steps can reproduce the bug?

• Install speckit
• Try to filter for commands using partial name like /plan

What is the expected behavior?

/plan provides /prompts:speckit.plan

Additional information

_No response_