(webui) REFACTOR: UI primitives and polish (#19551)

* webui: UI primitives and polish (non-MCP)

* chore: update webui build output

tools/server/webui/src/lib/utils/index.ts

@@ -93,3 +93,6 @@ export { getLanguageFromFilename } from './syntax-highlight-language';
 
 // Text file utilities
 export { isTextFileByName, readFileAsText, isLikelyTextFile } from './text-files';
+
+// Image error fallback utilities
+export { getImageErrorFallbackHtml } from './image-error-fallback';