feat: 图片预览与发送全量实现 (#31~#35)

- #31 ImageMessageBubble: typ=2 气泡，max 220pt / min 80pt 尺寸规则，进度环叠层
- #32 ImageViewerPage: photo_view 全屏查看，PhotoViewGallery 多图滑动，保存+分享工具栏
- #33 ImagePickerSheet + SendImageUseCase: 相册/相机选图(最多9张)，裁剪，dart:ui 解析宽高，FormData CDN 上传，typ=2 发送
- #34 image_cropper 接入：_PreviewTile 点击裁剪，iOS TOCropViewController 对齐
- #35 _MessageBubble BubbleKind 路由：typ switch → 各媒体气泡，输入栏新增附件按钮

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/im_app/lib/features/chat/di/chat_service_providers.dart

@@ -6,6 +6,7 @@ import 'package:im_app/core/services/ws_message_service.dart';
 import 'package:im_app/features/chat/di/chat_provider.dart';
 import 'package:im_app/features/chat/di/message_provider.dart';
 import 'package:im_app/features/chat/usecases/fetch_history_use_case.dart';
+import 'package:im_app/features/chat/usecases/send_image_usecase.dart';
 import 'package:im_app/features/chat/usecases/send_message_use_case.dart';
 
 /// ## DI 装配：Chat 服务层
@@ -64,3 +65,13 @@ final fetchHistoryUseCaseProvider = Provider<FetchHistoryUseCase>((ref) {
     messageRepo: ref.read(messageRepositoryProvider),
   );
 });
+
+// ── SendImageUseCase ──────────────────────────────────────────────────────────
+
+/// 图片上传并发送消息用例 Provider（#33）
+final sendImageUseCaseProvider = Provider<SendImageUseCase>((ref) {
+  return SendImageUseCase(
+    apiClient: ref.read(networkSdkApiProvider),
+    sendMessage: ref.read(sendMessageUseCaseProvider),
+  );
+});