feat: Add temporary system prompt

Adds a new setting that allows users to set a temporary system prompt for the current chat.
This prompt will override the selected system prompt if it exists.
The new setting is available in the "Current Chat Model Settings" modal.
This feature provides a way to quickly experiment with different system prompts without having to change the default setting.

src/assets/locale/zh/common.json

@@ -85,6 +85,11 @@
             "numGpu": {
                 "label": "Num GPU",
                 "placeholder": "输入要发送到 GPU 的层数"
+            },
+            "systemPrompt": {
+                "label": "临时系统提示",
+                "placeholder": "输入系统提示",
+                "help": "这是一种在当前聊天中快速设置系统提示的方法，如果存在已选择的系统提示，它将覆盖该提示。"
             }
         },
         "advanced": "更多模型设置"