feat(tablet): cap wide-layout margins at 80dp so content uses the screen

lib/screens/track_metadata_screen.dart

@@ -20,6 +20,7 @@ import 'package:spotiflac_android/services/platform_bridge.dart';
 import 'package:spotiflac_android/services/ffmpeg_service.dart';
 import 'package:spotiflac_android/services/replaygain_service.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
+import 'package:spotiflac_android/utils/adaptive_layout.dart';
 import 'package:spotiflac_android/utils/audio_conversion_utils.dart';
 import 'package:spotiflac_android/utils/audio_format_utils.dart';
 import 'package:spotiflac_android/utils/cover_art_utils.dart';
@@ -659,7 +660,11 @@ class _TrackMetadataScreenState extends ConsumerState<TrackMetadataScreen>
             SliverToBoxAdapter(
               child: Center(
                 child: ConstrainedBox(
-                  constraints: const BoxConstraints(maxWidth: 720),
+                  constraints: BoxConstraints(
+                    maxWidth: adaptiveContentMaxWidth(
+                      MediaQuery.sizeOf(context).width,
+                    ),
+                  ),
                   child: _buildAnimatedTrackContent(context, ref, colorScheme),
                 ),
               ),

lib/utils/adaptive_layout.dart

@@ -1,15 +1,25 @@
 import 'package:flutter/widgets.dart';
 
-/// Horizontal inset that centers content of [maxWidth] at [contentMaxWidth];
-/// zero once it fits, so rows stop stretching across a wide surface. Prefer
-/// this constraint-based form when the widget may live inside an already
-/// clamped box (e.g. a bottom sheet), where screen width would over-inset.
-double wideInsetForWidth(double maxWidth, {double contentMaxWidth = 720}) =>
-    maxWidth > contentMaxWidth ? (maxWidth - contentMaxWidth) / 2 : 0;
+/// Widest content span for a surface of [maxWidth]: content is never narrower
+/// than [contentMaxWidth], and the centering margin never exceeds 80dp per
+/// side — so tablets keep near-full-width rows (issue #493) instead of a
+/// fixed 720dp column floating in whitespace.
+double adaptiveContentMaxWidth(
+  double maxWidth, {
+  double contentMaxWidth = 720,
+}) => maxWidth > contentMaxWidth + 160 ? maxWidth - 160 : contentMaxWidth;
 
-/// Horizontal inset that centers full-width list content at [contentMaxWidth]
-/// on tablets/landscape; zero on phones, so rows stop stretching across the
-/// whole screen.
+/// Horizontal inset that centers content of [maxWidth] at
+/// [adaptiveContentMaxWidth]; zero once it fits. Prefer this constraint-based
+/// form when the widget may live inside an already clamped box (e.g. a bottom
+/// sheet), where screen width would over-inset.
+double wideInsetForWidth(double maxWidth, {double contentMaxWidth = 720}) =>
+    maxWidth > contentMaxWidth
+    ? ((maxWidth - contentMaxWidth) / 2).clamp(0.0, 80.0)
+    : 0;
+
+/// Horizontal inset that centers full-width list content on tablets/landscape;
+/// zero on phones, so rows stop stretching across the whole screen.
 double wideListInset(BuildContext context, {double contentMaxWidth = 720}) =>
     wideInsetForWidth(
       MediaQuery.sizeOf(context).width,