Autocomplete incorrectly prioritizes custom slash commands over built-in commands

Problem

When typing built-in slash commands like /clear, the autocomplete system highlights and suggests custom project commands with similar prefixes (like /clean) instead. This causes users to accidentally trigger the wrong command.

Steps to Reproduce

1. Have a custom slash command defined (e.g., /clean in .claude/commands/clean.md)
2. Type /clear (a built-in command) in the Claude Code terminal
3. Observe that /clean is highlighted at the bottom as a suggestion
4. Pressing Enter may trigger /clean instead of /clear

Expected Behavior

• Built-in commands should be prioritized over custom commands in autocomplete
• Or autocomplete should require more specific matching to avoid conflicts
• Or both options should be clearly shown with built-in commands marked distinctly

Actual Behavior

Custom commands with similar prefixes override/shadow built-in commands in the autocomplete suggestions, making it difficult to use built-in functionality.

Impact

Users cannot reliably use built-in commands when custom commands have similar names, leading to frustration and accidental command execution.