test: add E2E tests for markdown shortcuts in editor (#224)

[zacharias-ona]

Closes #224

What

Adds E2E Playwright tests verifying that Lexical's MarkdownShortcutPlugin correctly transforms markdown syntax as the user types in the editor.

Tests added

Shortcut	Expected result	Verified
# at line start	Converts to <h1>	✅
> at line start	Converts to <blockquote>	✅
- at line start	Converts to <ul><li>	✅
``` + Space	Converts to <code> block	✅

Each test creates a fresh page via navigateToEditorPage, types the markdown shortcut, then asserts the DOM element type changed and typed content renders inside the new block.

How

• Follows existing E2E patterns from editor-slash-commands.spec.ts and editor-toolbar.spec.ts
• Uses authenticatedPage fixture and navigateToEditorPage helper
• Uses unique Date.now() markers to avoid matching pre-existing content

Testing

• pnpm lint ✅
• pnpm typecheck ✅
• pnpm test — 252 unit tests pass ✅
• pnpm test:e2e — 66 E2E tests pass (including 4 new) ✅

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Project	Deployment	Actions	Updated (UTC)
memo	Ready	Preview, Comment	Apr 18, 2026 7:58am

[zacharias-ona]

✅ UI verification skipped — no UI files changed. This PR only adds E2E tests (e2e/editor-markdown-shortcuts.spec.ts).

[zacharias-ona]

✅ Post-merge verification skipped — test: PR does not affect the live app.