feat(canvas-studio): add product empty states

[SunilKumarKV]

Summary

Adds product-grade empty states and onboarding guidance across Canvas Studio.

Added

• Canvas empty state with starter actions
• Template CTAs from empty canvas
• Layers empty state
• Properties empty state
• Code panel guidance state
• Better first-use UX

Validation

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

Manual QA

• /studio loads ✅
• Empty canvas CTA works ✅
• Template CTA works ✅
• Layers empty state works ✅
• Properties empty state works ✅
• Existing chore(deps): bump github/codeql-action from 3 to 4 #1–feat: Issue #52 Design System Foundation #52 features still work ✅
• No console errors ✅