feat(offline+post): Offline Mode Overhaul & Post Details Screen Redesign (v2.2.0)

lib/backend/services/downloaded_media_service.dart

@@ -48,4 +48,39 @@ class DownloadedMediaService {
   Future<Result<void>> clearMissingFiles() => _repository.clearMissingFiles();
 
   Future<Result<int>> count() => _repository.count();
+
+  static int getFileSizeSync(DownloadedMedia media) {
+    if (media.savedPath.isEmpty) return 0;
+    final file = File(media.savedPath);
+    if (!file.existsSync()) return 0;
+    try {
+      return file.lengthSync();
+    } catch (_) {
+      return 0;
+    }
+  }
+
+  static Future<int> totalDiskSizeBytes(Iterable<DownloadedMedia> items) async {
+    int total = 0;
+    for (final media in items) {
+      if (media.savedPath.isNotEmpty) {
+        final file = File(media.savedPath);
+        if (await file.exists()) {
+          try {
+            total += await file.length();
+          } catch (_) {}
+        }
+      }
+    }
+    return total;
+  }
+
+  static String formatBytes(int bytes) {
+    if (bytes < 1024) return '$bytes B';
+    if (bytes < 1024 * 1024) return '${(bytes / 1024).toStringAsFixed(1)} KB';
+    if (bytes < 1024 * 1024 * 1024) {
+      return '${(bytes / (1024 * 1024)).toStringAsFixed(1)} MB';
+    }
+    return '${(bytes / (1024 * 1024 * 1024)).toStringAsFixed(2)} GB';
+  }
 }