fix: ReadEvent incompatible sse data format

internal/models/chat/sse_reader.go

@@ -47,6 +47,12 @@ func (r *SSEReader) ReadEvent() (*SSEEvent, error) {
 			return &SSEEvent{Data: []byte(jsonStr)}, nil
 		}
 
+		// 增强兼容性(data:后面没有紧接着一个空格)
+		if strings.HasPrefix(line, "data:") {
+			jsonStr := line[5:]
+			return &SSEEvent{Data: []byte(jsonStr)}, nil
+		}
+
 		// 其他行（如 event:, id: 等）跳过
 	}