feat(redpacket): 红包与游戏横幅全量实现 (#19~#24)

- #19 fix: SendRedEnvelopeUseCase 动态取 currencyType（workspaceId>0 取
  workspace.currency，修复 iOS 硬编码 PEA → 150001 错误）
- #20: RedEnvelopeBubble typ=8，四态（橙色领取/已领/过期/抢完）+ 领取按钮
- #21: ReceiveRedEnvelopeUseCase POST /app/api/wallet/rp/receive，
  typed JSON body（避免 code=30007），SnackBar 反馈
- #22: SendRedEnvelopeSheet BottomSheet，STANDARD_RP + LUCKY_RP，
  发送成功后构建 typ=8 content JSON 回调给 ChatPage
- #23: BannerViewModel Notifier，Group.topic 双格式解析（JSON object/string），
  FetchBannerUseCase + Timer 倒计时 + applyNewRound WS 接口
- #24: BannerView 游戏横幅条（状态/倒计时/上期结果），
  MiniAppFloatButton 悬浮按钮（hasGame 显示/隐藏，onTap TODO #25）

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

apps/im_app/lib/features/chat/usecases/fetch_banner_usecase.dart

@@ -0,0 +1,16 @@
+import 'package:networks_sdk/networks_sdk.dart';
+
+import 'package:im_app/data/remote/red_envelope_request.dart';
+
+/// 获取游戏横幅 UseCase
+///
+/// 对应 Gitea issue #23 / iOS BannerViewModel.loadBanner()
+class FetchBannerUseCase {
+  final NetworksSdkApi _api;
+
+  const FetchBannerUseCase({required NetworksSdkApi api}) : _api = api;
+
+  Future<GameBannerData?> execute(String gameId) async {
+    return _api.executeRequest(FetchBannerRequest(gameId: gameId));
+  }
+}

apps/im_app/lib/features/chat/usecases/receive_red_envelope_usecase.dart

@@ -0,0 +1,74 @@
+import 'package:networks_sdk/networks_sdk.dart';
+
+import 'package:im_app/data/remote/red_envelope_request.dart';
+
+/// 领取红包结果
+class ReceiveRpResult {
+  final bool success;
+  final String amount;
+  final int rpStatus;
+  final String displayMessage;
+
+  const ReceiveRpResult({
+    required this.success,
+    required this.amount,
+    required this.rpStatus,
+    required this.displayMessage,
+  });
+}
+
+/// 领取红包 UseCase
+///
+/// 对应 Gitea issue #21 / iOS RedEnvelopeDetailSheet.claim()
+///
+/// ⚠️ `ReceiveRpRequest` 使用 JSON typed body（非 form string），
+/// 服务端要求 bool/int 为原生类型，否则返回 code=30007。
+class ReceiveRedEnvelopeUseCase {
+  final NetworksSdkApi _api;
+
+  const ReceiveRedEnvelopeUseCase({required NetworksSdkApi api}) : _api = api;
+
+  Future<ReceiveRpResult> execute({
+    required String rpId,
+    required int chatId,
+    required String rpType,
+    required int messageId,
+  }) async {
+    final result = await _api.executeRequest(
+      ReceiveRpRequest(
+        rpId: rpId,
+        chatId: chatId,
+        rpType: rpType,
+        sendRpMsgId: messageId,
+      ),
+    );
+
+    if (result == null) {
+      return const ReceiveRpResult(
+        success: false,
+        amount: '0',
+        rpStatus: 0,
+        displayMessage: '领取失败',
+      );
+    }
+
+    final msg = _statusMessage(result.grabFlag, result.rpStatus, result.amount);
+    return ReceiveRpResult(
+      success: result.grabFlag,
+      amount: result.amount,
+      rpStatus: result.rpStatus,
+      displayMessage: msg,
+    );
+  }
+
+  String _statusMessage(bool grabbed, int status, String amount) {
+    if (grabbed) return '领取成功！获得 $amount';
+    return switch (status) {
+      2 => '您已领取过该红包',
+      3 => '红包已过期',
+      4 => '手慢了，红包已抢完',
+      5 => '不在领取范围内',
+      _ => '领取失败',
+    };
+  }
+}

apps/im_app/lib/features/chat/usecases/send_red_envelope_usecase.dart

@@ -0,0 +1,83 @@
+import 'package:networks_sdk/networks_sdk.dart';
+
+import 'package:im_app/data/remote/red_envelope_request.dart';
+
+/// 发送红包 UseCase
+///
+/// 对应 Gitea issue #19 + #22
+///
+/// ## currencyType 动态化（#19 bug fix）
+///
+/// - `workspaceId > 0`：先请求 `/workspace/workspace/get` 取 workspace.currency（如 USDT）
+/// - `workspaceId == 0`：默认 `"PEA"`
+///
+/// iOS 老项目硬编码 `currencyType=PEA`，导致 workspace 群报错 150001。
+///
+/// ## 成功后调用方需要
+///
+/// 使用返回的 `rpId` 构建 typ=8 消息 content，通过 ChatViewModel.sendMessage() 发送。
+class SendRedEnvelopeUseCase {
+  final NetworksSdkApi _api;
+
+  const SendRedEnvelopeUseCase({required NetworksSdkApi api}) : _api = api;
+
+  /// 发送红包，返回 rpId
+  ///
+  /// [chatId] 会话 ID
+  /// [chatType] 1=私聊 / 2=群聊
+  /// [workspaceId] 群 workspaceId（0 表示非工作台群）
+  /// [rpType] "STANDARD_RP" | "LUCKY_RP"（初期支持，后续扩展 MINE_RP / NN_RP）
+  /// [amount] 总金额字符串，如 "10.00"
+  /// [rpNum] 红包数量
+  /// [remark] 红包祝福语
+  Future<String> execute({
+    required int chatId,
+    required int chatType,
+    required int workspaceId,
+    required String rpType,
+    required String amount,
+    required int rpNum,
+    required String remark,
+  }) async {
+    // #19 fix: 根据 workspaceId 动态决定 currencyType
+    final currencyType = await _resolveCurrencyType(workspaceId);
+
+    final result = await _api.executeRequest(
+      SendRpRequest(
+        amount: amount,
+        currencyType: currencyType,
+        chatId: chatId,
+        chatType: chatType,
+        rpType: rpType,
+        recipientIds: const [],
+        rpNum: rpNum,
+        remark: remark,
+        msgSendTime: DateTime.now().microsecondsSinceEpoch,
+      ),
+    );
+
+    if (result == null || result.rpId.isEmpty) {
+      throw Exception('发送红包失败：未返回 rpId');
+    }
+    return result.rpId;
+  }
+
+  /// 根据 workspaceId 解析 currencyType
+  ///
+  /// - `workspaceId > 0` → 请求 workspace 取 currency 字段
+  /// - `workspaceId == 0` → 直接返回 "PEA"
+  Future<String> _resolveCurrencyType(int workspaceId) async {
+    if (workspaceId <= 0) return 'PEA';
+
+    try {
+      final ws = await _api.executeRequest(
+        GetWorkspaceRequest(workspaceId: workspaceId),
+      );
+      final currency = ws?.currency ?? '';
+      return currency.isNotEmpty ? currency : 'PEA';
+    } catch (_) {
+      // 降级：取不到 workspace 信息时使用默认值
+      return 'PEA';
+    }
+  }
+}