feat(export): add Markdown and HTML result export formats

[koraysrn]

Summary

Adds Markdown and HTML result export formats to both shells (Studio.tsx and
StudioWorkspace.tsx). Both formats follow the shared value contract of the existing CSV
exporter, so a value that appears one way in the grid and the CSV reads the same way in the
Markdown table and the HTML table.

Closes #1532

What changed

• New writers:
  • src/lib/export/markdown.ts renders a pipe table with a header row and a --- separator row.
  • src/lib/export/html.ts renders a complete standalone document: a <table> inside a minimal
    HTML shell with embedded CSS.
• ResultExportFormat gains markdown and html. Both are text formats, so they use the existing
  ResultExportFile shape and are written through downloadText.
• BottomPanel.tsx offers both formats in the Export menu and in the Copy-to-clipboard menu.
• Studio.tsx and StudioWorkspace.tsx keep one shared buildExportSource per shell, so masking
  and agent-artifact hydration apply to the new formats exactly as they apply to CSV, JSON and the
  SQL formats.

Value rendering

Both writers reuse the shared cell contract (renderValue in src/lib/export/csv.ts):

• null and undefined become an empty cell.
• Date values become their ISO string.
• Binary values become the same \x hex the grid and CSV show.
• Objects become jsonText, which is bigint-safe and cycle-safe.
• Everything else becomes String(value).

Escaping

• Markdown escapes \ and | in every cell and header cell, and replaces \n and \r with
  <br> so a cell value cannot break the table row.
• HTML escapes &, <, >, " and ' in every cell and header cell.

Empty results

• No columns: empty output for both formats.
• Columns known but no rows: the header row is still written.

Tests

• tests/unit/lib/export/markdown.test.ts (17 tests): escaping, header and separator rows,
  newline handling and the empty-result matrix.
• tests/unit/lib/export/html.test.ts (14 tests): entity escaping, the standalone document shape
  and the empty-result matrix.
• tests/unit/lib/export/result-export.test.ts gains Markdown and HTML integration coverage
  through buildResultExport.
• tests/unit/components/bottom-panel-formats.test.ts pins the shared format list.
• tests/components/studio/bottom-panel-export-formats.test.tsx (13 tests) pins the Export and
  Copy menu items across dialects.

Verification

• bun run typecheck: clean
• bun run lint: 0 errors
• bun run knip: clean
• bun run build: succeeds
• Changed unit and component tests pass (603 tests across the export and shell suites)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!

[cevheri]

Thanks, this works well in both shells and the escaping holds up. I pushed a small commit: FEATURES.md now lists Markdown and HTML, and a blank line inside a cell keeps its own
.