add chinese subtitles

ios/OralTrainer/Services/SentenceBoundaryAPI.swift

@@ -46,6 +46,26 @@ struct SentenceExplanationResponse: Decodable {
     }
 }
 
+struct SubtitleTranslationItem: Decodable {
+    let index: Int
+    let zhText: String
+
+    private enum CodingKeys: String, CodingKey {
+        case index
+        case zhText = "zh_text"
+    }
+}
+
+struct SubtitleTranslationResponse: Decodable {
+    let videoHash: String
+    let translations: [SubtitleTranslationItem]
+
+    private enum CodingKeys: String, CodingKey {
+        case translations
+        case videoHash = "video_hash"
+    }
+}
+
 extension SentenceBoundaryAPI {
     static func explain(
         _ sentence: SentenceBoundary,
@@ -79,4 +99,32 @@ extension SentenceBoundaryAPI {
             .decode(SentenceExplanationResponse.self, from: result.body)
             .explanation
     }
+
+    static func translateSubtitles(videoHash: String) async throws -> [Int: String] {
+        let hash = videoHash.lowercased()
+        guard hash.range(of: AppConfig.sha256Pattern, options: .regularExpression) != nil else {
+            throw SentenceBoundaryAPIError.invalidHash
+        }
+        var headers: [String: String] = ["Accept": "application/json"]
+        if !AppConfig.authToken.isEmpty {
+            headers["Authorization"] = "Bearer \(AppConfig.authToken)"
+        }
+        let result = try await HTTPClient.execute(
+            baseURL: AppConfig.serverBaseURL,
+            path: "api/v1/videos/\(hash)/subtitle-translation",
+            method: "POST",
+            timeout: AppConfig.translationTimeout,
+            headers: headers
+        )
+        guard (200...299).contains(result.statusCode) else {
+            let detail = String(data: result.body, encoding: .utf8) ?? ""
+            throw HTTPClientError.badStatus(result.statusCode, detail)
+        }
+        let payload = try JSONDecoder().decode(SubtitleTranslationResponse.self, from: result.body)
+        var mapped: [Int: String] = [:]
+        for item in payload.translations where !item.zhText.isEmpty {
+            mapped[item.index] = item.zhText
+        }
+        return mapped
+    }
 }