added ios module

ios/OralTrainer/Services/SentenceBoundaryAPI.swift

@@ -0,0 +1,34 @@
+import Foundation
+
+enum SentenceBoundaryAPIError: LocalizedError {
+    case invalidHash
+    case hashMismatch
+
+    var errorDescription: String? {
+        switch self {
+        case .invalidHash:
+            return "video_hash 必须是 64 位 SHA-256 十六进制字符串"
+        case .hashMismatch:
+            return "服务端返回的句边界哈希与请求不一致"
+        }
+    }
+}
+
+enum SentenceBoundaryAPI {
+    static func fetch(videoHash: String) async throws -> SentenceBoundaryDocument {
+        let hash = videoHash.lowercased()
+        guard hash.range(of: AppConfig.sha256Pattern, options: .regularExpression) != nil else {
+            throw SentenceBoundaryAPIError.invalidHash
+        }
+        let result = try await HTTPClient.getJSON(
+            SentenceBoundaryDocument.self,
+            baseURL: AppConfig.serverBaseURL,
+            path: "api/v1/videos/\(hash)/sentence-boundaries",
+            timeout: AppConfig.readTimeout
+        )
+        guard result.value.videoHash.lowercased() == hash else {
+            throw SentenceBoundaryAPIError.hashMismatch
+        }
+        return result.value
+    }
+}