Streamlines the command suggestion interface and fixes list auto-completion behavior:

- Remove command descriptions for cleaner suggestion popup UI
- Replace PaperclipIcon with FileIcon for semantic accuracy
- Fix list auto-completion to avoid extra newline when exiting list mode
- Add explanatory comments for cursor offset positions
- Improve dependency array in useListAutoCompletion hook

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Co-Authored-By: Claude <noreply@anthropic.com>