refactor(providers): move UI-declared providers to lib/providers

The listening summary and system volume providers lived in UI files.
They move verbatim to lib/providers with the same names; the old files
re-export them so tests and other importers are unchanged.

lib/providers/listening_statistics_provider.dart

@@ -0,0 +1,14 @@
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:spotiflac_android/services/listening_statistics.dart';
+
+final listeningSummaryProvider = FutureProvider.autoDispose
+    .family<ListeningSummary, ({int days, int year})>((ref, period) async {
+      await listeningRecorder.flush();
+      final now = DateTime.now();
+      final tomorrow = DateTime(now.year, now.month, now.day + 1);
+      final start = period.days == 0
+          ? DateTime(period.year)
+          : DateTime(now.year, now.month, now.day - period.days + 1);
+      final end = period.days == 0 ? DateTime(period.year + 1) : tomorrow;
+      return ListeningStatisticsStore.instance.load(start, end);
+    });

lib/providers/system_volume_provider.dart

@@ -0,0 +1,35 @@
+import 'dart:async';
+
+import 'package:flutter_riverpod/flutter_riverpod.dart';
+import 'package:spotiflac_android/services/music_playback_deck.dart';
+import 'package:spotiflac_android/services/system_volume_service.dart';
+import 'package:volume_controller/volume_controller.dart';
+
+final usbVolumeProvider = StreamProvider.autoDispose<UsbVolumeState?>((ref) {
+  final events = StreamController<UsbVolumeState?>();
+  void changed() => events.add(usbHardwareVolume.value);
+  usbHardwareVolume.addListener(changed);
+  changed();
+  ref.onDispose(() {
+    usbHardwareVolume.removeListener(changed);
+    unawaited(events.close());
+  });
+  return events.stream;
+});
+
+/// A single shared subscription for the visible player, including hardware
+/// volume-button changes. This controls system volume, not ReplayGain gain.
+final systemVolumeProvider = StreamProvider.autoDispose<double>(
+  (ref) => SystemVolumeService.instance.changes,
+);
+
+final systemVolumeWriterProvider = Provider<Future<void> Function(double)>((
+  ref,
+) {
+  return (value) {
+    if (usbHardwareVolume.value != null) return setUsbHardwareVolume(value);
+    final volume = VolumeController.instance;
+    volume.showSystemUI = false;
+    return volume.setVolume(value.clamp(0, 1));
+  };
+});

lib/screens/listening_statistics_screen.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:intl/intl.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/providers/listening_statistics_provider.dart';
 import 'package:spotiflac_android/providers/settings_provider.dart';
 import 'package:spotiflac_android/screens/listening_rewind_screen.dart';
 import 'package:spotiflac_android/services/listening_statistics.dart';
@@ -22,17 +23,7 @@ import 'package:spotiflac_android/widgets/app_sliver_header.dart';
 import 'package:spotiflac_android/widgets/player_artwork.dart';
 import 'package:spotiflac_android/widgets/settings_group.dart';
 
-final listeningSummaryProvider = FutureProvider.autoDispose
-    .family<ListeningSummary, ({int days, int year})>((ref, period) async {
-      await listeningRecorder.flush();
-      final now = DateTime.now();
-      final tomorrow = DateTime(now.year, now.month, now.day + 1);
-      final start = period.days == 0
-          ? DateTime(period.year)
-          : DateTime(now.year, now.month, now.day - period.days + 1);
-      final end = period.days == 0 ? DateTime(period.year + 1) : tomorrow;
-      return ListeningStatisticsStore.instance.load(start, end);
-    });
+export 'package:spotiflac_android/providers/listening_statistics_provider.dart';
 
 class ListeningStatisticsScreen extends ConsumerStatefulWidget {
   const ListeningStatisticsScreen({super.key});

lib/widgets/player_volume_control.dart

@@ -4,43 +4,15 @@ import 'package:flutter/cupertino.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/providers/system_volume_provider.dart';
 import 'package:spotiflac_android/theme/mornye_theme.dart';
 import 'package:spotiflac_android/widgets/app_icon.dart';
 import 'package:spotiflac_android/widgets/app_slider.dart';
 import 'package:spotiflac_android/widgets/mornye_player_slider.dart';
 import 'package:spotiflac_android/utils/logger.dart';
-import 'package:volume_controller/volume_controller.dart';
 import 'package:spotiflac_android/services/music_playback_deck.dart';
-import 'package:spotiflac_android/services/system_volume_service.dart';
 
-final usbVolumeProvider = StreamProvider.autoDispose<UsbVolumeState?>((ref) {
-  final events = StreamController<UsbVolumeState?>();
-  void changed() => events.add(usbHardwareVolume.value);
-  usbHardwareVolume.addListener(changed);
-  changed();
-  ref.onDispose(() {
-    usbHardwareVolume.removeListener(changed);
-    unawaited(events.close());
-  });
-  return events.stream;
-});
-
-/// A single shared subscription for the visible player, including hardware
-/// volume-button changes. This controls system volume, not ReplayGain gain.
-final systemVolumeProvider = StreamProvider.autoDispose<double>(
-  (ref) => SystemVolumeService.instance.changes,
-);
-
-final systemVolumeWriterProvider = Provider<Future<void> Function(double)>((
-  ref,
-) {
-  return (value) {
-    if (usbHardwareVolume.value != null) return setUsbHardwareVolume(value);
-    final volume = VolumeController.instance;
-    volume.showSystemUI = false;
-    return volume.setVolume(value.clamp(0, 1));
-  };
-});
+export 'package:spotiflac_android/providers/system_volume_provider.dart';
 
 /// System (or USB hardware) volume slider for the player and USB settings.
 /// Mornye draws its glass slider between speaker glyphs; Material draws the