feat: add visual separator between thinking content and response (AstrBotDevs#8059)

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

Author: Pleiades1726

astrbot/core/pipeline/result_decorate/stage.py

@@ -289,7 +289,9 @@ async def process(
                         ),
                     )
                 else:
-                    result.chain.insert(0, Plain(f"🤔 思考: {reasoning_content}\n"))
+                    result.chain.insert(
+                        0, Plain(f"🤔 思考: {reasoning_content}\n\n────\n")
+                    )
 
             if should_tts and tts_provider:
                 new_chain = []