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>

routers/web/repo/render.go

@@ -43,7 +43,8 @@ func RenderFile(ctx *context.Context) {
 		CurrentRefPath:  ctx.Repo.RefTypeNameSubURL(),
 		CurrentTreePath: path.Dir(ctx.Repo.TreePath),
 	}).WithRelativePath(ctx.Repo.TreePath).WithStandalonePage(markup.StandalonePageOptions{
-		CurrentWebTheme: ctx.TemplateContext.CurrentWebTheme(),
+		CurrentWebTheme:   ctx.TemplateContext.CurrentWebTheme(),
+		RenderQueryString: ctx.Req.URL.RawQuery,
 	})
 	renderer, rendererInput, err := rctx.DetectMarkupRendererByReader(blobReader)
 	if err != nil {