Layer 4: Cupertino chrome polish

[lmist]

Summary

• Vibrancy materials: Tab bar and statusbar use backdrop-filter: blur(20px) saturate(1.2) with semi-transparent backgrounds via color-mix, matching macOS native title bar behavior. Toolbar gets consistent blur/saturate treatment.
• Tighter proportions: Tab bar 42→38px, statusbar 42→32px, reclaiming 20px for content. All chrome elements (vim badge, pickers, keyboard button) proportionally reduced.
• Refined surfaces: All borders thinned to 0.5px (Apple separator weight). Tabs use 6px radius instead of 999px pills. Active tab shadow reduced from 0 8px 24px to 0 0.5px 2.5px. Modal gets three-layer Apple shadow. Scrollbar thinned with semi-transparent thumb. Editor pane's redundant inset shadow removed.

Test plan

• pnpm tauri dev — verify tab bar vibrancy blurs content behind it
• Switch all 3 themes — chrome surfaces adapt correctly
• Resize panes, open modal, create tabs — layout math correct with new heights
• Check traffic light alignment with new 80px left padding

🤖 Generated with Claude Code