feat(download): estimate file sizes in quality picker

lib/widgets/download_service_picker.dart

@@ -6,11 +6,17 @@ import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:spotiflac_android/providers/extension_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/utils/audio_format_utils.dart';
+import 'package:spotiflac_android/utils/download_size_estimate.dart';
+import 'package:spotiflac_android/utils/string_utils.dart';
 
 class DownloadServicePicker extends ConsumerStatefulWidget {
   final String? trackName;
   final String? artistName;
   final String? coverUrl;
+
+  /// Combined duration for the tracks being queued; null if any is unknown.
+  final Duration? duration;
   final void Function(String quality, String service) onSelect;
   final String? recommendedService;
 
@@ -19,6 +25,7 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
     this.trackName,
     this.artistName,
     this.coverUrl,
+    this.duration,
     required this.onSelect,
     this.recommendedService,
   });
@@ -32,6 +39,7 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
     String? trackName,
     String? artistName,
     String? coverUrl,
+    Duration? duration,
     String? recommendedService,
     required void Function(String quality, String service) onSelect,
   }) {
@@ -49,6 +57,7 @@ class DownloadServicePicker extends ConsumerStatefulWidget {
         trackName: trackName,
         artistName: artistName,
         coverUrl: coverUrl,
+        duration: duration,
         onSelect: onSelect,
         recommendedService: recommendedService,
       ),
@@ -120,6 +129,21 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
     final downloadExtensions = _downloadExtensions();
     final hasProviders = downloadExtensions.isNotEmpty;
     final qualityOptions = _getQualityOptions(downloadExtensions);
+    final settings = ref.watch(settingsProvider);
+    final convertedSize = settings.autoConvertDownloads
+        ? estimateDownloadSize(
+            duration: widget.duration,
+            quality: QualityOption(
+              id: 'converted',
+              label: '',
+              sizeEstimate: QualitySizeEstimate(
+                bitrateKbps: autoConvertBitrateKbps(
+                  settings.autoConvertBitrate,
+                ),
+              ),
+            ),
+          )
+        : null;
 
     return SafeArea(
       child: SingleChildScrollView(
@@ -191,12 +215,40 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
                 _QualityOption(
                   title: _localizedQualityLabel(context, quality),
                   subtitle: _localizedQualityDescription(context, quality),
+                  estimatedSize: _sizeLabel(
+                    context,
+                    estimateDownloadSize(
+                      duration: widget.duration,
+                      quality: quality,
+                    ),
+                  ),
                   icon: _getQualityIcon(quality.id),
                   onTap: () {
                     Navigator.pop(context);
                     widget.onSelect(quality.id, _selectedService);
                   },
                 ),
+              if (qualityOptions.isNotEmpty)
+                Padding(
+                  padding: const EdgeInsets.fromLTRB(24, 8, 24, 0),
+                  child: Text(
+                    [
+                      context.l10n.downloadSizeEstimateNote,
+                      if (convertedSize != null)
+                        context.l10n.downloadConvertedSizeEstimate(
+                          displayFormatForLossyFormat(
+                            normalizeAutoConvertFormat(
+                              settings.autoConvertFormat,
+                            ),
+                          ),
+                          _sizeLabel(context, convertedSize),
+                        ),
+                    ].join('\n\n'),
+                    style: Theme.of(context).textTheme.bodySmall?.copyWith(
+                      color: colorScheme.onSurfaceVariant,
+                    ),
+                  ),
+                ),
             ],
 
             const SizedBox(height: 16),
@@ -206,6 +258,14 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
     );
   }
 
+  String _sizeLabel(BuildContext context, DownloadSizeEstimate? estimate) {
+    if (estimate == null) return context.l10n.downloadSizeUnavailable;
+    final size = estimate.minBytes == estimate.maxBytes
+        ? formatBytes(estimate.maxBytes)
+        : '${formatBytes(estimate.minBytes)}–${formatBytes(estimate.maxBytes)}';
+    return context.l10n.downloadEstimatedSize(size);
+  }
+
   IconData _getQualityIcon(String qualityId) {
     final normalized = qualityId.toUpperCase();
     if (normalized.startsWith('MP3_') || normalized == 'MP3') {
@@ -260,12 +320,14 @@ class _DownloadServicePickerState extends ConsumerState<DownloadServicePicker> {
 class _QualityOption extends StatelessWidget {
   final String title;
   final String subtitle;
+  final String estimatedSize;
   final IconData icon;
   final VoidCallback onTap;
 
   const _QualityOption({
     required this.title,
     required this.subtitle,
+    required this.estimatedSize,
     required this.icon,
     required this.onTap,
   });
@@ -284,12 +346,20 @@ class _QualityOption extends StatelessWidget {
         child: Icon(icon, color: colorScheme.onPrimaryContainer, size: 20),
       ),
       title: Text(title, style: const TextStyle(fontWeight: FontWeight.w500)),
-      subtitle: subtitle.isNotEmpty
-          ? Text(
+      subtitle: Column(
+        crossAxisAlignment: CrossAxisAlignment.start,
+        children: [
+          if (subtitle.isNotEmpty)
+            Text(
               subtitle,
               style: TextStyle(color: colorScheme.onSurfaceVariant),
-            )
-          : null,
+            ),
+          Text(
+            estimatedSize,
+            style: TextStyle(color: colorScheme.onSurfaceVariant),
+          ),
+        ],
+      ),
       onTap: onTap,
     );
   }

lib/widgets/track_detail_actions.dart

@@ -7,6 +7,7 @@ import 'package:spotiflac_android/providers/extension_provider.dart';
 import 'package:spotiflac_android/providers/library_collections_provider.dart';
 import 'package:spotiflac_android/providers/local_library_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
+import 'package:spotiflac_android/utils/download_size_estimate.dart';
 import 'package:spotiflac_android/utils/logger.dart';
 import 'package:spotiflac_android/widgets/download_service_picker.dart';
 import 'package:spotiflac_android/widgets/view_queue_snackbar_action.dart';
@@ -35,6 +36,7 @@ void downloadSingleTrack(
       trackName: track.name,
       artistName: track.artistName,
       coverUrl: track.coverUrl,
+      duration: Duration(seconds: track.duration),
       recommendedService: recommendedService,
       onSelect: (quality, service) {
         ref
@@ -218,6 +220,7 @@ Future<void> queueTracksSkippingDownloaded(
       context,
       trackName: '${tracksToQueue.length} tracks',
       artistName: artistNameForPicker,
+      duration: totalDownloadDuration(tracksToQueue),
       recommendedService: recommendedService,
       onSelect: (quality, service) {
         ref