fix(export): render HTML tables and preserve vertical alignment

[murongg]

Raw HTML tables were escaped by the shared preview renderer, so HTML and PDF exports printed HTML source instead of a table. Render block HTML through the editor's existing sanitizer and preserve vertical-align so merged cells honor authored alignment in the editor, preview, and export.

Regression tests cover merged rows and columns, HTML blocks inside quotes and lists, image path resolution, unsafe HTML filtering, document updates, and editor recreation. Fenced HTML remains code. No new dependencies or changes to authored Markdown are required.

Closes #750

Validation

• pnpm --filter @markra/editor test -- src/raw-html-sanitize.test.ts src/codemirror/html-table-widget.test.ts src/codemirror/raw-html-preview.test.ts — 58 tests passed.
• pnpm --filter @markra/app test -- src/components/MarkdownExportDocument.test.tsx src/components/MarkdownPreviewDocument.test.tsx src/lib/document-export.test.ts — 24 tests passed.
• pnpm --filter @markra/app typecheck:test and pnpm --filter @markra/editor typecheck:test — passed.
• pnpm build — all workspace builds passed, including desktop and web bundles and the desktop vendor chunk check.
• Headless Chrome QA with synthetic data: merged cells were vertically centered in the editor, preview, and exported document; click/blur preserved Markdown; no browser errors. Inspected screenshots and the rendered PDF page, and confirmed the PDF contains a real table rather than HTML source.

Windows native export was not run on this macOS host; the shared export renderer and Chromium PDF output were verified.

[vercel]

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Project	Deployment	Actions	Updated
markra-web	Ready	Preview	Oct 4, 2026 3:30pm UTC