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/browse.html

@@ -22,6 +22,8 @@
       <option value="react-ts">React + TS</option>
       <option value="vue">Vue</option>
       <option value="svelte">Svelte</option>
+      <option value="markdown">Markdown</option>
+      <option value="wasm">WASM</option>
     </select>
     <select id="filter-sort">
       <option value="updated">Recently Updated</option>