feat: placeholder的不同状态显示

frontend/src/components/workspace/input-box.tsx

@@ -659,7 +659,11 @@ export function InputBox({
               !effectiveIsFocused && "h-[80px] py-0 leading-20",
             )}
             disabled={isInputDisabled}
-            placeholder={t.inputBox.placeholder}
+            placeholder={
+              showWelcomeStyle
+                ? t.inputBox.welcomePlaceholder
+                : t.inputBox.chatPlaceholder
+            }
             autoFocus={autoFocus}
             defaultValue={initialValue}
             onFocus={() => setIsFocused(true)}

frontend/src/core/i18n/locales/en-US.ts

@@ -77,6 +77,9 @@ export const enUS: Translations = {
   // Input Box
   inputBox: {
     placeholder: "How can I assist you today?",
+    welcomePlaceholder:
+      "Start chatting directly, or describe your task and pick a skill for professional execution.",
+    chatPlaceholder: "Type “@” to reference files.",
     createSkillPrompt:
       "We're going to build a new skill step by step with `skill-creator`. To start, what do you want this skill to do?",
     sendMessagePrice:

frontend/src/core/i18n/locales/types.ts

@@ -70,6 +70,8 @@ export interface Translations {
   inputBox: {
     sendMessagePrice: string;
     placeholder: string;
+    welcomePlaceholder: string;
+    chatPlaceholder: string;
     createSkillPrompt: string;
     addAttachments: string;
     history: string;

frontend/src/core/i18n/locales/zh-CN.ts

@@ -78,7 +78,9 @@ export const zhCN: Translations = {
 
   // Input Box
   inputBox: {
-    placeholder: "可直接对话; 或输入需求并选择skill，完成专业任务;“@”可引用文件",
+    placeholder: "可直接对话; 或输入需求并选择skill，完成专业任务;",
+    welcomePlaceholder: "可直接对话; 或输入需求并选择skill，完成专业任务;",
+    chatPlaceholder: "“@”可引用文件。",
     createSkillPrompt:
       "我们一起用 skill-creator 技能来创建一个技能吧。先问问我希望这个技能能做什么。",
     sendMessagePrice: