Add Tailwind CSS toggle, Markdown/WASM modes, and npm import resolution

- Tailwind CSS: toolbar checkbox injects Play CDN into preview, persisted
  per-fiddle via new options JSON column
- Markdown mode: uses marked.js CDN, renders markdown to HTML preview with
  CSS tab for custom styling
- WASM mode: starter template with inline WebAssembly add function, supports
  top-level await via module detection
- npm imports: auto-detect bare import specifiers in module code and inject
  importmap pointing to esm.sh CDN
- Module auto-detection for html-css-js mode (import/export statements)
- DB migration adds options column, server passes through all API endpoints
- All features work across preview, export, and embed

public/js/browse.js

@@ -12,6 +12,8 @@ const JS_TYPE_LABELS = {
   'react-ts': 'React+TS',
   vue: 'Vue',
   svelte: 'Svelte',
+  markdown: 'MD',
+  wasm: 'WASM',
 };
 
 function relativeTime(dateStr) {