fix: preserve math through streaming HTML repair

Disable only Remend's incomplete-HTML stripping in message/tool content and reasoning rendering. Keep TeX, source data, and sanitization unchanged; unfinished HTML can display literally.

PR #266 identified the less-than comparison trigger. This uses an independently authored renderer configuration fix rather than its TeX-spacing workaround, with streaming, incremental, literal-code, and safety regressions.

components/ai-elements/reasoning.tsx

@@ -24,7 +24,7 @@ import {
 import { Streamdown } from "streamdown";
 
 import { transformMathDelimiters } from "@/src/core";
-import { streamdownPlugins } from "./message";
+import { streamdownPlugins, streamdownRemend } from "./message";
 import { mdComponents } from "@/components/md-blocks";
 import { Shimmer } from "./shimmer";
 
@@ -209,7 +209,7 @@ export const ReasoningContent = memo(
       )}
       {...props}
     >
-      <Streamdown components={mdComponents} plugins={streamdownPlugins}>
+      <Streamdown components={mdComponents} plugins={streamdownPlugins} remend={streamdownRemend}>
         {transformMathDelimiters(children)}
       </Streamdown>
     </CollapsibleContent>