The default max tokens of 215 is too small, answers are often cut off.I will modify it to 512 to address this issue. (#845)

### What problem does this PR solve?

### Type of change

- [x] Refactoring

web/src/constants/knowledge.ts

@@ -31,14 +31,14 @@ export const settledModelVariableMap = {
     top_p: 0.3,
     frequency_penalty: 0.7,
     presence_penalty: 0.4,
-    max_tokens: 215,
+    max_tokens: 512,
   },
   [ModelVariableType.Balance]: {
     temperature: 0.5,
     top_p: 0.5,
     frequency_penalty: 0.7,
     presence_penalty: 0.4,
-    max_tokens: 215,
+    max_tokens: 512,
   },
 };