feat(ios): IOS-M0-06 + IOS-M0-07

- LearningSessionService 新增 list() 分页查询
- FileUploadService 新增 deleteFile() 调用 DELETE /files/:id

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

AIStudyApp/AIStudyApp/Core/Services/APIService.swift

@@ -210,6 +210,13 @@ class LearningSessionService {
     func end(id: String) async throws -> LearningSession {
         return try await client.request("/learning-sessions/\(id)/end", method: "POST")
     }
+
+    func list(page: Int = 1, limit: Int = 20) async throws -> [LearningSession] {
+        return try await client.request("/learning-sessions", queryItems: [
+            URLQueryItem(name: "page", value: String(page)),
+            URLQueryItem(name: "limit", value: String(limit)),
+        ])
+    }
 }
 
 // MARK: - Review

AIStudyApp/AIStudyApp/Core/Services/FileUploadService.swift

@@ -74,6 +74,11 @@ class FileUploadService {
         return confirmResp.id
     }
 
+    /// 删除文件（COS + 数据库）
+    func deleteFile(fileId: String) async throws {
+        let _: GenericSuccessResponse = try await client.request("/files/\(fileId)", method: "DELETE")
+    }
+
     /// 获取文件下载 URL
     func getDownloadUrl(fileId: String) async throws -> String {
         let detail: FileDetailResponse = try await client.request("/files/\(fileId)")