refactor: differentiate reference marker handling between stream and non-stream modes

- Stream: strip both and [reference:N] markers to prevent
  leaking partial link metadata during incremental output
- Non-stream: convert citation/reference markers to Markdown links for
  Claude Messages, Gemini generateContent, and OpenAI Chat/Responses
- Remove StripReferenceMarkers option from call sites; behavior is now
  determined automatically by stream vs non-stream context
- Extend JS runtime stripReferenceMarkersText() to also match [citation:N]
- Add tests for streaming marker stripping and non-stream link conversion

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/js/chat-stream/sse_parse_impl.js

@@ -621,7 +621,7 @@ function stripReferenceMarkersText(text) {
   if (!text) {
     return text;
   }
-  return text.replace(/\[reference:\s*\d+\]/gi, '');
+  return text.replace(/\[(?:citation|reference):\s*\d+\]/gi, '');
 }
 
 function asString(v) {