feat(app-shell): move to editor-first global UX

[SunilKumarKV]

Summary

Reworks the RainbowCode shell into a compact editor-first global product UX.

Why

The previous redesign still felt like decorative cards. This update moves the app toward a real design/editor workflow: compact chrome, focused canvas, dedicated inspector, and reduced marketing-style layout.

Added

• Compact command-style topbar
• Editor-grade left navigation
• Focused canvas workspace
• Dedicated inspector column
• Compact code preview panel
• Reduced hero/card visual noise
• Better canvas-first hierarchy

Validation

• pnpm typecheck ✅
• pnpm build ✅
• pnpm lint ✅
• pnpm test ✅

Manual QA

• /studio loads ✅
• Canvas appears once ✅
• Existing chore(deps): bump github/codeql-action from 3 to 4 #1–feat: Issue #52 Design System Foundation #52 features still work ✅
• Theme Studio still works ✅
• Component Studio still works ✅
• Canvas tools still work ✅
• No console errors ✅