fix(ui+permission): 移除联合投稿 / emoji换SVG / 修复移动端浅色适配 / 已排期显示日期 / 隐藏.env提示 / 公开排期档期游客访问

具体改动：

1. feat(投稿表单): 移除 RequestForm.vue 联合投稿功能整套模板+状态+payload+CSS(10处残留)

2. feat(图标): Icon.vue 新增 sparkles/star 图标; 首页档期卡片📅🎵✨和排期列表空状态🎵📅换成 lucide SVG Icon

3. fix(浅色适配): ScheduleList.vue 日期选择弹窗桌面端+移动端(content/header/h3/close-btn/item)全部改为 bg-primary + var text + indigo 主色, 修复竖屏选择日期标题白字看不见

4. feat(歌曲列表): SongList.vue scheduled-tag 内联追加 formatScheduleDate, 徽章+日期双胶囊显示

5. fix(登录): OAuthButtons.vue showPlaceholderHint 强制 false, 隐藏虚线框 .env 配置提示

6. fix(权限): server/middleware/auth.ts + auth-route-policy.ts 双白名单同步追加 /api/expected-play-dates GET 公共访问, 修复未登录 Authentication expired 401

server/utils/auth-route-policy.ts

@@ -33,6 +33,7 @@ export const PUBLIC_API_EXACT_ROUTES: readonly RoutePolicy[] = [
   { path: '/api/auth/captcha', methods: GET_METHODS },
   { path: '/api/semesters/current', methods: GET_METHODS },
   { path: '/api/play-times', methods: GET_METHODS },
+  { path: '/api/expected-play-dates', methods: GET_METHODS },
   { path: '/api/schedules/public', methods: GET_METHODS },
   { path: '/api/songs/count', methods: GET_METHODS },
   { path: '/api/songs/public', methods: GET_METHODS },