Frontend iframe renderer framework: 3D models, OpenAPI (#37233)

Introduces a frontend external-render framework that runs renderer
plugins inside an `iframe` (loaded via `srcdoc` to keep the CSP
`sandbox` directive working without origin-related console noise), and
migrates the 3D viewer and OpenAPI/Swagger renderers onto it. PDF and
asciicast paths are refactored to share the same `data-render-name`
mechanism.

Adds e2e coverage for 3D, PDF, asciicast and OpenAPI render paths, plus
a regression for the `RefTypeNameSubURL` double-escape on non-ASCII
branch names.

Signed-off-by: silverwind <me@silverwind.io>
Co-authored-by: Claude (Opus 4.6) <noreply@anthropic.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/public/manifest.go

@@ -56,6 +56,8 @@ func parseManifest(data []byte) (map[string]string, map[string]string) {
 		paths[key] = entry.File
 		names[entry.File] = entry.Name
 		// Map associated CSS files, e.g. "css/index.css" -> "css/index.B3zrQPqD.css"
+		// FIXME: INCORRECT-VITE-MANIFEST-PARSER: the logic is wrong, Vite manifest doesn't work this way
+		// It just happens to be correct for the current modules dependencies
 		for _, css := range entry.CSS {
 			cssKey := path.Dir(css) + "/" + entry.Name + path.Ext(css)
 			paths[cssKey] = css