Add 8 E2E test suites for release sanity coverage
83 new tests across 8 files:
- design-panel: selection → properties panel, fill/stroke/effect add, visibility toggle, multi-select
- code-panel: JSX output, OpenPencil/Tailwind toggle, copy button, empty state
- components: create component (⌘⌥K), create instance, propagation, detach
- copy-paste: store copy/paste, ⌘D duplicate, cut, multi-select duplicate
- multi-page: add/switch/delete pages, rename, last-page protection
- text-editing: text tool, text node creation, typography section, frame tool
- keyboard-shortcuts: all 9 tool keys, ⌘A/Escape/Backspace, ]/[, ⌘G/⌘⇧G, ⌘\, ⌘Z/⌘⇧Z
- context-menu: right-click items, duplicate/visibility/lock/delete/group/component, Copy as submenu
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