Group system and project commands separately in the / command picker

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When typing / in the chat, system commands (e.g. /help, /clear, /compact) and project-level custom commands (from .claude/commands/) are shown in a flat mixed list. As teams add more custom commands, this becomes hard to scan.

Proposed Solution

Add visual grouping or category labels in the command picker to separate:

System commands — built-in Claude Code commands
Project commands — commands from .claude/commands/ in the repo

Alternative Solutions

_No response_

Priority

Critical - Blocking my work

Feature Category

CLI commands and flags

Use Case Example

Why it matters:
Teams using Claude Code collaboratively add custom commands for workflows (e.g. Jira ticket generation, PR review, deploy helpers). Mixing these with system commands adds cognitive overhead when picking the right command, especially for new team members onboarding to a project.

Suggested UI:
A simple section header/divider between the two groups in the picker dropdown would be sufficient.

Additional Context

_No response_