fix(app): poster sheet close button — header row with explicit close (drag-down not obvious on long sheet)

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

apps/mobile/lib/l10n/app_en.arb

@@ -426,5 +426,6 @@
   "sharePosterMode": "Generate QR poster",
   "posterDownload": "Download poster image",
   "posterSaved": "Poster saved to gallery",
-  "posterSaveFailed": "Failed to save poster"
+  "posterSaveFailed": "Failed to save poster",
+  "close": "Close"
 }

apps/mobile/lib/l10n/app_localizations.dart

@@ -2011,6 +2011,12 @@ abstract class AppLocalizations {
   /// In zh, this message translates to:
   /// **'海报保存失败'**
   String get posterSaveFailed;
+
+  /// No description provided for @close.
+  ///
+  /// In zh, this message translates to:
+  /// **'关闭'**
+  String get close;
 }
 
 class _AppLocalizationsDelegate

apps/mobile/lib/l10n/app_localizations_en.dart

@@ -1028,4 +1028,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get posterSaveFailed => 'Failed to save poster';
+
+  @override
+  String get close => 'Close';
 }

apps/mobile/lib/l10n/app_localizations_zh.dart

@@ -995,4 +995,7 @@ class AppLocalizationsZh extends AppLocalizations {
 
   @override
   String get posterSaveFailed => '海报保存失败';
+
+  @override
+  String get close => '关闭';
 }

apps/mobile/lib/l10n/app_zh.arb

@@ -426,5 +426,6 @@
   "sharePosterMode": "生成二维码海报",
   "posterDownload": "下载海报图",
   "posterSaved": "海报已保存到相册",
-  "posterSaveFailed": "海报保存失败"
+  "posterSaveFailed": "海报保存失败",
+  "close": "关闭"
 }

apps/mobile/lib/pages/share_qr_dialog.dart

@@ -52,7 +52,8 @@ typedef ShareLauncher = Future<void> Function(String text);
 
 final shareLauncherProvider = Provider<ShareLauncher>(
   // share_plus 11：SharePlus.instance.share（旧 Share.share 已废弃）。
-  (ref) => (text) async => SharePlus.instance.share(
+  (ref) =>
+      (text) async => SharePlus.instance.share(
         ShareParams(text: text, subject: text.split('\n').first),
       ),
 );
@@ -332,6 +333,22 @@ class _PosterSheetState extends ConsumerState<_PosterSheet> {
           child: Column(
             mainAxisSize: MainAxisSize.min,
             children: [
+              // ── 头行：标题 + 显式关闭（海报较长时下拉手势不明显）──
+              Row(
+                children: [
+                  Expanded(
+                    child: Text(
+                      l10n.sharePosterMode,
+                      style: theme.textTheme.titleMedium,
+                    ),
+                  ),
+                  IconButton(
+                    tooltip: l10n.close,
+                    icon: const Icon(Icons.close),
+                    onPressed: () => Navigator.of(context).pop(),
+                  ),
+                ],
+              ),
               // ── 海报（整块 RepaintBoundary；下载即渲染此区域）──
               RepaintBoundary(
                 key: _posterKey,