feat: add jj-aware statusline with setup/remove commands

[muloka]

Summary

• Add statusline-jj.sh — jj-aware statusline script showing model, change ID, bookmark, description, trunk state (@trunk, +N, ⎇), context %, and cost
• Add /statusline-jj-setup command — copies script and wires statusLine in .claude/settings.local.json
• Add /statusline-jj-remove command — removes statusline config and script
• Includes repo-state caching to avoid redundant jj queries
• Graceful fallback for non-jj directories

Test plan

• Tested statusline output for all three trunk states (+N, @trunk, ⎇)
• Tested setup flow (copy script + add settings key)
• Tested remove flow (delete settings key + remove script)
• Tested non-jj fallback

🤖 Generated with Claude Code