feat: 仪表盘布局重排，新增题图上传能力

frontend/src/services/dashboardService.js

@@ -0,0 +1,38 @@
+import http from './http'
+
+/**
+ * 获取当前题图设置
+ * @returns {Promise<{cover_path: string|null, episode_number: number|null, episode_title: string|null}>}
+ */
+export async function getCurrentCover() {
+  const response = await http.get('/dashboard/cover')
+  return response.data
+}
+
+/**
+ * 上传题图（仅制片人/责编可用）
+ * @param {File} file - 海报图片文件
+ * @param {number} episodeNumber - 关联期次号
+ * @param {string} episodeTitle - 关联期次节目名
+ * @returns {Promise<{success: boolean, cover_path: string}>}
+ */
+export async function uploadCover(file, episodeNumber, episodeTitle) {
+  const formData = new FormData()
+  formData.append('file', file)
+  formData.append('episode_number', String(episodeNumber))
+  formData.append('episode_title', episodeTitle)
+  const response = await http.post('/dashboard/cover', formData, {
+    headers: { 'Content-Type': 'multipart/form-data' },
+  })
+  return response.data
+}
+
+/**
+ * 获取未来排播计划
+ * @param {number} limit - 返回条数，默认6
+ * @returns {Promise<Array<{episode_number, program_name, planned_air_date, editor_name_snapshot}>>}
+ */
+export async function getUpcomingSchedules(limit = 6) {
+  const response = await http.get('/schedules/upcoming', { params: { limit } })
+  return response.data
+}