fix: remove /think trigger, add back <think> in clean_text

- Removed /think trigger from prompt (model generates better without it)
- Added <think> and </think> back to clean_text (model uses plain text
  thinking tags, not special tokens)

src/application/chat/use_cases.rs

@@ -89,8 +89,8 @@ pub fn build_prompt(messages: &[ChatMessage], tools: &Option<Vec<ToolDef>>) -> S
         }
     }
 
-    // Generation prompt: thinking mode (MiniCPM5 native)
-    prompt.push_str("<|im_start|>assistant\n/think\n\n");
+    // Generation prompt
+    prompt.push_str("<|im_start|>assistant\n");
     prompt
 }
 
@@ -187,6 +187,8 @@ pub fn clean_text(text: &str) -> String {
         .replace("<|tool_call|>", "")
         .replace("<|execute_start|>", "")
         .replace("<|execute_end|>", "")
+        .replace("<think>", "")
+        .replace("</think>", "")
         .replace("/think", "")
         .replace("/no_think", "")
         .trim()