feat: 新增 Starlight 周年庆彩蛋（每年 10 月 4 日）

10 月 4 日（Starlight 首个发布日 2014-10-04）当天，启动器顶部显示周年横幅并飘落蛋糕/彩带，周年数按年份-2014 计算。新增 helpers/anniversary.ts 与 AnniversaryCelebration.vue；开发者页加入 force_anniversary_celebration 功能开关用于随时预览。

apps/app-frontend/src/locales/en-US/index.json

@@ -11428,5 +11428,8 @@
   },
   "app.settings.synced-options.game-settings.value-unset": {
     "message": "Choose a value"
+  },
+  "app.anniversary.banner": {
+    "message": "Happy {ordinal} Anniversary, Starlight!"
   }
 }

apps/app-frontend/src/locales/zh-CN/index.json

@@ -11350,5 +11350,6 @@
 	"app.settings.synced-options.game-settings.value-mixed": { "message": "各实例不同" },
 	"app.settings.synced-options.game-settings.value-off": { "message": "关闭" },
 	"app.settings.synced-options.game-settings.value-on": { "message": "开启" },
-	"app.settings.synced-options.game-settings.value-unset": { "message": "选择一个值" }
+	"app.settings.synced-options.game-settings.value-unset": { "message": "选择一个值" },
+	"app.anniversary.banner": { "message": "Starlight {ordinal} 周年快乐！" }
 }