Optimize WebUI streaming and long history rendering

Batch stream deltas, window long transcripts, lazy-load syntax highlighting, and refine activity/composer interactions.

Add title refresh retries plus tests for streaming, windowing, code blocks, and live activity behavior.

webui/src/types/react-syntax-highlighter-subpaths.d.ts

@@ -0,0 +1,22 @@
+declare module "react-syntax-highlighter/dist/esm/prism-async-light" {
+  import * as React from "react";
+  import type { SyntaxHighlighterProps } from "react-syntax-highlighter";
+
+  export default class SyntaxHighlighter extends React.Component<SyntaxHighlighterProps> {
+    static registerLanguage(name: string, func: unknown): void;
+  }
+}
+
+declare module "react-syntax-highlighter/dist/esm/styles/prism/one-dark" {
+  import type * as React from "react";
+
+  const style: { [key: string]: React.CSSProperties };
+  export default style;
+}
+
+declare module "react-syntax-highlighter/dist/esm/styles/prism/one-light" {
+  import type * as React from "react";
+
+  const style: { [key: string]: React.CSSProperties };
+  export default style;
+}