* perf: enhance chat components with theme and fullscreen toggles
- Added theme and fullscreen toggle functionality to Chat.vue and ConversationSidebar.vue.
- Introduced a new StyledMenu component for improved dropdown menus.
- Updated MessageList.vue and ChatInput.vue for better mobile responsiveness and UI consistency.
- Enhanced language switcher integration in ConversationSidebar.vue.
- Added new settings translations in English and Chinese locales.
* fix: streamline conversation selection handling in Chat.vue
- Updated handleSelectConversation function to immediately set the current session ID and selected sessions, reducing the need for multiple clicks.
- Adjusted padding in ConversationSidebar.vue for improved layout consistency.
Soulter