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/js-preprocessors.js

@@ -3,6 +3,7 @@ import { loadScript } from './utils.js';
 let tsLoaded = false;
 let babelLoaded = false;
 let svelteLoaded = false;
+let markedLoaded = false;
 
 async function ensureTypeScript() {
   if (tsLoaded) return;
@@ -31,6 +32,19 @@ async function ensureBabel() {
   babelLoaded = true;
 }
 
+async function ensureMarked() {
+  if (markedLoaded) return;
+  await loadScript('https://cdnjs.cloudflare.com/ajax/libs/marked/15.0.7/marked.min.js');
+  if (typeof marked === 'undefined') {
+    await new Promise((resolve) => {
+      const check = setInterval(() => {
+        if (typeof marked !== 'undefined') { clearInterval(check); resolve(); }
+      }, 50);
+    });
+  }
+  markedLoaded = true;
+}
+
 async function ensureSvelte() {
   if (svelteLoaded) return;
   await loadScript('https://unpkg.com/svelte@4.2.19/compiler.cjs');
@@ -45,8 +59,10 @@ export async function compileJs(code, mode) {
   if (!code.trim()) return { js: '' };
 
   switch (mode) {
-    case 'html-css-js':
-      return { js: code };
+    case 'html-css-js': {
+      const isModule = /(?:^|\n)\s*(?:import\s|export\s)/m.test(code);
+      return { js: code, isModule };
+    }
 
     case 'typescript':
       return compileTypeScript(code);
@@ -63,6 +79,16 @@ export async function compileJs(code, mode) {
     case 'svelte':
       return compileSvelte(code);
 
+    case 'markdown':
+      return compileMarkdown(code);
+
+    case 'wasm': {
+      // WASM starter uses top-level await, always treat as module
+      const hasModuleSyntax = /(?:^|\n)\s*(?:import\s|export\s)/m.test(code);
+      const hasTopLevelAwait = /(?:^|\n)\s*(?:const|let|var)\s+.*=\s*await\b/m.test(code) || /(?:^|\n)\s*await\s/m.test(code);
+      return { js: code, isModule: hasModuleSyntax || hasTopLevelAwait };
+    }
+
     default:
       return { js: code };
   }
@@ -125,6 +151,12 @@ function compileVue(code) {
   return { js, extraCss };
 }
 
+async function compileMarkdown(code) {
+  await ensureMarked();
+  const renderedHtml = marked.parse(code);
+  return { js: '', renderedHtml };
+}
+
 async function compileSvelte(code) {
   await ensureSvelte();
   const result = svelte.compile(code, {
@@ -185,6 +217,12 @@ export function getFrameworkRuntime(mode) {
         bodyHtml: '<div id="app"></div>',
       };
 
+    case 'markdown':
+      return { scripts: [], bodyHtml: '' };
+
+    case 'wasm':
+      return { scripts: [], bodyHtml: '' };
+
     default:
       return { scripts: [], bodyHtml: '' };
   }