feat: multi-tab support in MainArea

- Refactor MainArea: tabs array + activeTabId (was single activeTab)
- Open/close tabs dynamically, status tab not closable
- Tab opener buttons (keys/cli/slowlog/memory) in top-right
- Right-click context menu: close/closeOthers/closeRight/closeLeft
- Mouse wheel cycling through tabs
- Scrollable tab bar with hidden scrollbar
- i18n keys for tab context menu (zh-CN + en)

src/i18n/locales/zh-CN.ts

@@ -20,6 +20,12 @@ export default {
     subtitle: '现代 Redis 桌面管理器',
     placeholder: '选择或创建连接开始使用',
   },
+  tab: {
+    close: '关闭',
+    closeOthers: '关闭其他',
+    closeRight: '关闭右侧',
+    closeLeft: '关闭左侧',
+  },
   connection: {
     title: '连接',
     new: '新建连接',