refactor: Update message hint text for improved user guidance

- Changed the placeholder text in the message input field across multiple languages to "Ask Conduit" for better clarity and user engagement.
- Updated localization files for German, English, Spanish, French, Italian, Dutch, Russian, and Chinese to reflect the new hint text.

lib/l10n/app_zh.arb

@@ -141,7 +141,7 @@
   "voiceActionStart": "开始",
   "messageInputLabel": "消息输入",
   "messageInputHint": "输入您的消息",
-  "messageHintText": "消息...",
+  "messageHintText": "问 Conduit",
   "stopGenerating": "停止生成",
   "codeCopiedToClipboard": "代码已复制到剪贴板。",
   "send": "发送",