Summary

• add a browser-specific entrypoint and build config (src/browser.ts, vite.config.browser.ts)
• add browser build scripts/exports in package.json
• add browser examples and docs for client-side usage
• make direct-open (file://) examples and test pages work via UMD (window.wiremd)
• render previews through iframe.srcdoc so style/theme CSS applies correctly
• improve browser editor UX (format tab readability, textarea vertical sizing)

Validation

• npm run build
• npm run build:browser

Closes #75