Ship file viewer, editor improvements, and private package releases

examples/basic-app/public/viewer/sample.html

@@ -0,0 +1,5 @@
+<!doctype html>
+<html lang="en">
+  <title>HTML source preview</title>
+  <body><h1>HTML preview in a sandbox</h1><p>Use Source to inspect this document. Scripts and external resources are disabled.</p></body>
+</html>