feat(aiCore): 添加对文本增量累积的可配置支持

根据模型是否支持文本增量来决定是否累积文本内容，新增accumulate参数控制行为

src/renderer/src/aiCore/chunk/AiSdkToChunkAdapter.ts

@@ -28,11 +28,14 @@ export interface CherryStudioChunk {
  */
 export class AiSdkToChunkAdapter {
   toolCallHandler: ToolCallChunkHandler
+  private accumulate: boolean | undefined
   constructor(
     private onChunk: (chunk: Chunk) => void,
-    mcpTools: MCPTool[] = []
+    mcpTools: MCPTool[] = [],
+    accumulate?: boolean
   ) {
     this.toolCallHandler = new ToolCallChunkHandler(onChunk, mcpTools)
+    this.accumulate = accumulate
   }
 
   /**
@@ -95,7 +98,11 @@ export class AiSdkToChunkAdapter {
         })
         break
       case 'text-delta':
-        final.text += chunk.text || ''
+        if (this.accumulate) {
+          final.text += chunk.text || ''
+        } else {
+          final.text = chunk.text || ''
+        }
         this.onChunk({
           type: ChunkType.TEXT_DELTA,
           text: final.text || ''

src/renderer/src/aiCore/index_new.ts

@@ -43,10 +43,12 @@ export default class ModernAiProvider {
   private legacyProvider: LegacyAiProvider
   private config: ReturnType<typeof providerToAiSdkConfig>
   private actualProvider: Provider
+  private model: Model
 
   constructor(model: Model, provider?: Provider) {
     this.actualProvider = provider || getActualProvider(model)
     this.legacyProvider = new LegacyAiProvider(this.actualProvider)
+    this.model = model
 
     // 只保存配置，不预先创建executor
     this.config = providerToAiSdkConfig(this.actualProvider, model)
@@ -237,7 +239,8 @@ export default class ModernAiProvider {
         topicId: config.topicId
       })
 
-      const adapter = new AiSdkToChunkAdapter(config.onChunk, config.mcpTools)
+      const accumulate = this.model.supported_text_delta !== false // true and undefined
+      const adapter = new AiSdkToChunkAdapter(config.onChunk, config.mcpTools, accumulate)
 
       logger.debug('Final params before streamText', {
         modelId,