feat(f7): sealed webview asset + esbuild preview bundle (#21)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

esbuild.mjs

@@ -30,13 +30,30 @@ const liveTurnOptions = {
   logLevel: "info",
 };
 
+/** @type {import('esbuild').BuildOptions} */
+const previewOptions = {
+  entryPoints: ["media/preview.ts"],
+  outfile: "out/media/preview.js",
+  bundle: true,
+  // The webview is a browser context; mermaid is bundled IN (and ONLY in) this
+  // asset so it never bloats the extension-host bundle (the @cline/sdk size
+  // discipline). No externals — everything is shipped to the sealed webview.
+  platform: "browser",
+  format: "iife",
+  target: "es2020",
+  sourcemap: true,
+  logLevel: "info",
+};
+
 if (watch) {
   const ctx = await context(options);
   const ctxLive = await context(liveTurnOptions);
-  await Promise.all([ctx.watch(), ctxLive.watch()]);
+  const ctxPreview = await context(previewOptions);
+  await Promise.all([ctx.watch(), ctxLive.watch(), ctxPreview.watch()]);
   console.log("esbuild: watching…");
 } else {
   await build(options);
   await build(liveTurnOptions);
-  console.log("esbuild: build complete → out/extension.cjs + out/liveTurn.mjs");
+  await build(previewOptions);
+  console.log("esbuild: build complete → out/extension.cjs + out/liveTurn.mjs + out/media/preview.js");
 }