feat: implement initial language resolution for SSR and local storage support

- Added a function to determine the initial language based on server-side rendering and local storage.
- Updated i18n initialization to use the resolved initial language instead of the default.

src/lib/player-viewport.ts

@@ -0,0 +1,9 @@
+/** H5 玩家端逻辑宽度（px），桌面浏览器居中展示为「手机画布」 */
+export const PLAYER_VIEWPORT_MAX_PX = 480;
+
+/** 内容列：全宽但不超过手机逻辑宽度，水平居中 */
+export const playerViewportColumnClass = "mx-auto w-full max-w-[480px]" as const;
+
+/** 贴底/贴顶固定栏：与内容列同宽并居中（桌面不铺满整屏） */
+export const playerViewportFixedBarClass =
+  "fixed left-1/2 z-50 w-full max-w-[480px] -translate-x-1/2" as const;