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>

eslint.config.ts

@@ -924,6 +924,7 @@ export default defineConfig([
   {
     ...playwright.configs['flat/recommended'],
     files: ['tests/e2e/**/*.test.ts'],
+    languageOptions: {globals: {...globals.nodeBuiltin, ...globals.browser}},
     rules: {
       ...playwright.configs['flat/recommended'].rules,
       'playwright/expect-expect': [0],