feat(tablet): clamp remaining screens - settings, queue lists, wizard

- SettingsGroup centers itself at 720dp via its incoming constraint
  (not screen width, so groups inside clamped sheets are never
  over-inset; unbounded-width contexts guarded); priority scaffold,
  bespoke hero cards, and donate page get the same inset - all 18+
  settings pages clamp from shared widgets
- queue list-mode, local/downloaded album track lists, favorite
  artists, home recent-access, and extension detail sections adopt
  wideListInset like the screens fixed earlier
- track metadata content clamped at 720dp, which also tames the
  width-derived spectrogram height
- announcement dialog capped at 480dp wide; setup wizard and
  tutorial content at 560dp with a 400dp action button

lib/utils/adaptive_layout.dart

@@ -1,9 +1,17 @@
 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;
+
 /// Horizontal inset that centers full-width list content at [contentMaxWidth]
 /// on tablets/landscape; zero on phones, so rows stop stretching across the
 /// whole screen.
-double wideListInset(BuildContext context, {double contentMaxWidth = 720}) {
-  final width = MediaQuery.sizeOf(context).width;
-  return width > contentMaxWidth ? (width - contentMaxWidth) / 2 : 0;
-}
+double wideListInset(BuildContext context, {double contentMaxWidth = 720}) =>
+    wideInsetForWidth(
+      MediaQuery.sizeOf(context).width,
+      contentMaxWidth: contentMaxWidth,
+    );