feat(app,viewer): WeChat card share + 'Share to...' label + site og tags

- 按钮文字「分享到微信/其他应用」→「分享到...」（用户需求）
- 微信卡片分享（fluwx 6）：WECHAT_APPID 经 --dart-define 注入；已配置且
  装微信 → WXWebpage 卡片（标题=相册名、描述=日期·地点、缩略图=封面压缩
  240px PNG ≤32KB、点击进观众链接）；未配置/未装 → 回退系统分享面板
- viewer index.html 加站点级 og 标签（微信/QQ 抓取链接预览用；每相册动态
  og 需服务端注入，登记后续增强）
- 397/397 全绿、analyze 0

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

apps/mobile/lib/l10n/app_en.arb

@@ -422,7 +422,7 @@
   "bannerPickerHint": "Tap to pick a banner image (shown atop the viewer page)",
   "bannerSelected": "Banner selected — will upload on save",
   "bannerUploadFailed": "Banner upload failed",
-  "shareCardMode": "Share to WeChat / other apps",
+  "shareCardMode": "Share to...",
   "sharePosterMode": "Generate QR poster",
   "posterDownload": "Download poster image",
   "posterSaved": "Poster saved to gallery",

apps/mobile/lib/l10n/app_localizations.dart

@@ -1985,7 +1985,7 @@ abstract class AppLocalizations {
   /// No description provided for @shareCardMode.
   ///
   /// In zh, this message translates to:
-  /// **'分享到微信 / 其他应用'**
+  /// **'分享到...'**
   String get shareCardMode;
 
   /// No description provided for @sharePosterMode.

apps/mobile/lib/l10n/app_localizations_en.dart

@@ -1015,7 +1015,7 @@ class AppLocalizationsEn extends AppLocalizations {
   String get bannerUploadFailed => 'Banner upload failed';
 
   @override
-  String get shareCardMode => 'Share to WeChat / other apps';
+  String get shareCardMode => 'Share to...';
 
   @override
   String get sharePosterMode => 'Generate QR poster';

apps/mobile/lib/l10n/app_localizations_zh.dart

@@ -982,7 +982,7 @@ class AppLocalizationsZh extends AppLocalizations {
   String get bannerUploadFailed => '宣传图上传失败';
 
   @override
-  String get shareCardMode => '分享到微信 / 其他应用';
+  String get shareCardMode => '分享到...';
 
   @override
   String get sharePosterMode => '生成二维码海报';

apps/mobile/lib/l10n/app_zh.arb

@@ -422,7 +422,7 @@
   "bannerPickerHint": "点击选择宣传图（展示在观众页顶部）",
   "bannerSelected": "已选择宣传图——保存时上传",
   "bannerUploadFailed": "宣传图上传失败",
-  "shareCardMode": "分享到微信 / 其他应用",
+  "shareCardMode": "分享到...",
   "sharePosterMode": "生成二维码海报",
   "posterDownload": "下载海报图",
   "posterSaved": "海报已保存到相册",

apps/mobile/lib/main.dart

@@ -1,11 +1,19 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:fluwx/fluwx.dart';
 
 import 'app/app.dart';
 import 'app/locale_controller.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
+  // 微信 SDK（卡片分享）：WECHAT_APPID 经 --dart-define 注入（微信开放平台
+  // 注册的应用 ID）；未配置（空）时跳过注册——分享回退系统分享面板。
+  // Android 需保证打包签名与微信平台注册签名一致，否则拉不起微信。
+  const wechatAppId = String.fromEnvironment('WECHAT_APPID');
+  if (wechatAppId.isNotEmpty) {
+    await Fluwx().registerApi(appId: wechatAppId, doOnIOS: false);
+  }
   // 启动先读语言偏好再 runApp：首帧即正确语言（无「system 闪变」，
   // P3 Task 10）。读取失败由 readPersisted 内部兜底为 system。
   final localeChoice = await LocaleSettings.readPersisted();

apps/mobile/lib/pages/share_qr_dialog.dart

@@ -10,10 +10,12 @@ library;
 
 import 'dart:ui' as ui;
 
+import 'package:dio/dio.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:fluwx/fluwx.dart';
 import 'package:gal/gal.dart';
 import 'package:qr_flutter/qr_flutter.dart';
 import 'package:share_plus/share_plus.dart';
@@ -47,17 +49,72 @@ final urlLauncherProvider = Provider<UrlLauncher>(
       (url) => launchUrl(Uri.parse(url), mode: LaunchMode.externalApplication),
 );
 
-/// 系统分享注入点（生产=share_plus；测试 override）。
-typedef ShareLauncher = Future<void> Function(String text);
+/// 分享请求（卡片字段：微信 SDK 用全集；系统分享回退用 title+url）。
+class ShareCardRequest {
+  const ShareCardRequest({
+    required this.title,
+    required this.description,
+    required this.url,
+    this.thumbnailUrl,
+  });
+
+  final String title;
+  final String description;
+  final String url;
+
+  /// 卡片缩略图（封面 URL；null=无图，微信显示默认图标）。
+  final String? thumbnailUrl;
+}
+
+/// 分享注入点（生产：微信已配置且安装→WXWebpage 卡片；否则系统分享面板。
+/// 测试 override）。
+typedef ShareLauncher = Future<void> Function(ShareCardRequest card);
 
 final shareLauncherProvider = Provider<ShareLauncher>(
-  // share_plus 11：SharePlus.instance.share（旧 Share.share 已废弃）。
-  (ref) =>
-      (text) async => SharePlus.instance.share(
-        ShareParams(text: text, subject: text.split('\n').first),
-      ),
+  (ref) => (card) async {
+    const wechatAppId = String.fromEnvironment('WECHAT_APPID');
+    if (wechatAppId.isNotEmpty && await Fluwx().isWeChatInstalled) {
+      final thumb = await compressShareThumbnail(card.thumbnailUrl);
+      await Fluwx().share(
+        WeChatShareWebPageModel(
+          card.url,
+          title: card.title,
+          description: card.description,
+          thumbData: thumb,
+          scene: WeChatScene.session,
+        ),
+      );
+      return;
+    }
+    // 回退：系统分享面板（文本=标题+链接；接收应用自行渲染链接）。
+    // share_plus 11：SharePlus.instance.share（旧 Share.share 已废弃）。
+    await SharePlus.instance.share(
+      ShareParams(text: '${card.title}\n${card.url}', subject: card.title),
+    );
+  },
 );
 
+/// 微信卡片缩略图：下载→缩到 240px→PNG（微信 thumbData 限制 ≤32KB）。
+Future<Uint8List?> compressShareThumbnail(String? url) async {
+  if (url == null) return null;
+  try {
+    final resp = await Dio().get<List<int>>(
+      url,
+      options: Options(responseType: ResponseType.bytes),
+    );
+    final data = Uint8List.fromList(resp.data!);
+    final codec = await ui.instantiateImageCodec(data, targetWidth: 240);
+    final frame = await codec.getNextFrame();
+    final resized = await frame.image.toByteData(
+      format: ui.ImageByteFormat.png,
+    );
+    return resized?.buffer.asUint8List();
+  } on Object {
+    // 缩略图失败不阻塞分享（无图卡片仍可发）
+    return null;
+  }
+}
+
 /// 海报保存相册注入点（生产=gal；测试 override）。
 typedef PosterSaver = Future<void> Function(ui.Image image);
 
@@ -89,7 +146,28 @@ class ShareQrPage extends ConsumerWidget {
     String url,
     String title,
   ) async {
-    await ref.read(shareLauncherProvider)('$title\n$url');
+    final l10n = AppLocalizations.of(context);
+    final localeName = l10n.localeName;
+    final start = formatAlbumDateTime(
+      album.startAt,
+      album.timezone,
+      localeName,
+    );
+    final end = album.endAt == null
+        ? null
+        : formatAlbumDateTime(album.endAt!, album.timezone, localeName);
+    final dateRange = end == null ? start : '$start ~ $end';
+    final venue = albumDisplayVenue(album, localeName);
+    final description = venue == null ? dateRange : '$dateRange · $venue';
+    // 缩略图用封面（列表即有签名 URL，减少一次串行请求）。
+    await ref.read(shareLauncherProvider)(
+      ShareCardRequest(
+        title: title,
+        description: description,
+        url: url,
+        thumbnailUrl: album.cover?.url,
+      ),
+    );
   }
 
   @override