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>

web_src/js/markup/content.ts

@@ -3,13 +3,14 @@ import {initMarkupCodeMath} from './math.ts';
 import {initMarkupCodeCopy} from './codecopy.ts';
 import {initMarkupRenderAsciicast} from './asciicast.ts';
 import {initMarkupTasklist} from './tasklist.ts';
-import {registerGlobalSelectorFunc} from '../modules/observer.ts';
-import {initMarkupRenderIframe} from './render-iframe.ts';
+import {registerGlobalInitFunc, registerGlobalSelectorFunc} from '../modules/observer.ts';
+import {initExternalRenderIframe} from './render-iframe.ts';
 import {initMarkupRefIssue} from './refissue.ts';
 import {toggleElemClass} from '../utils/dom.ts';
 
 // code that runs for all markup content
 export function initMarkupContent(): void {
+  registerGlobalInitFunc('initExternalRenderIframe', initExternalRenderIframe);
   registerGlobalSelectorFunc('.markup', (el: HTMLElement) => {
     if (el.matches('.truncated-markup')) {
       // when the rendered markup is truncated (e.g.: user's home activity feed)
@@ -25,7 +26,6 @@ export function initMarkupContent(): void {
     initMarkupCodeMermaid(el);
     initMarkupCodeMath(el);
     initMarkupRenderAsciicast(el);
-    initMarkupRenderIframe(el);
     initMarkupRefIssue(el);
   });
 }