refactor(ui): unify sliver page headers

lib/widgets/app_sliver_header.dart

@@ -0,0 +1,108 @@
+import 'package:flutter/material.dart';
+import 'package:spotiflac_android/theme/app_tokens.dart';
+import 'package:spotiflac_android/utils/app_bar_layout.dart';
+
+/// The collapsing header used by every top-level tab and every settings-style
+/// sub-page.
+///
+/// This replaces five hand-rolled copies of the same `SliverAppBar` +
+/// `LayoutBuilder` + `FlexibleSpaceBar` block. Those copies had drifted into two
+/// type ramps (tab roots expanded the title to 34pt, sub-pages to 28pt); both
+/// now expand to [AppTokens.headerExpandedTitleSize], which matches the
+/// Material 3 large top app bar headline.
+class AppSliverHeader extends StatelessWidget {
+  /// Root of a navigation tab: no back button, and the title stays aligned with
+  /// the content margin at every collapse ratio.
+  const AppSliverHeader.tabRoot({super.key, required this.title, this.actions})
+    : leading = null,
+      _showLeading = false;
+
+  /// A pushed page: shows [leading] (a back button by default) and slides the
+  /// title clear of it as the header collapses.
+  const AppSliverHeader.page({
+    super.key,
+    required this.title,
+    this.actions,
+    this.leading,
+  }) : _showLeading = true;
+
+  final String title;
+  final List<Widget>? actions;
+
+  /// Overrides the default back button. Only used by the page variant.
+  final Widget? leading;
+
+  final bool _showLeading;
+
+  /// Left inset of the collapsed title when a leading button is present: enough
+  /// to clear a 48dp icon button plus the 8dp toolbar margin.
+  static const double _leadingClearance = 56;
+
+  /// Content margin the expanded title aligns to.
+  static const double _contentMargin = 24;
+
+  @override
+  Widget build(BuildContext context) {
+    final tokens = context.tokens;
+    final colorScheme = Theme.of(context).colorScheme;
+    final topPadding = normalizedHeaderTopPadding(context);
+    final maxHeight = tokens.headerExpandedHeight + topPadding;
+    final minHeight = kToolbarHeight + topPadding;
+
+    return SliverAppBar(
+      expandedHeight: maxHeight,
+      collapsedHeight: kToolbarHeight,
+      floating: false,
+      pinned: true,
+      backgroundColor: colorScheme.surface,
+      surfaceTintColor: Colors.transparent,
+      automaticallyImplyLeading: false,
+      leading: _showLeading
+          ? leading ??
+                IconButton(
+                  tooltip: MaterialLocalizations.of(context).backButtonTooltip,
+                  icon: const Icon(Icons.arrow_back),
+                  onPressed: () => Navigator.pop(context),
+                )
+          : null,
+      actions: actions,
+      flexibleSpace: LayoutBuilder(
+        builder: (context, constraints) {
+          final expandRatio =
+              ((constraints.maxHeight - minHeight) / (maxHeight - minHeight))
+                  .clamp(0.0, 1.0);
+          final leftPadding = _showLeading
+              ? _leadingClearance -
+                    ((_leadingClearance - _contentMargin) * expandRatio)
+              : _contentMargin;
+          final fontSize =
+              tokens.headerCollapsedTitleSize +
+              (tokens.headerExpandedTitleSize -
+                      tokens.headerCollapsedTitleSize) *
+                  expandRatio;
+
+          return FlexibleSpaceBar(
+            expandedTitleScale: 1.0,
+            titlePadding: EdgeInsets.only(
+              left: leftPadding,
+              right: tokens.gapLg,
+              bottom: tokens.gapLg,
+            ),
+            title: Text(
+              title,
+              // The title grows as the header expands; without a cap a long
+              // localized title overflowed instead of ellipsizing.
+              maxLines: 1,
+              overflow: TextOverflow.ellipsis,
+              style: TextStyle(
+                fontSize: fontSize,
+                fontWeight: FontWeight.bold,
+                color: colorScheme.onSurface,
+              ),
+            ),
+          );
+        },
+      ),
+    );
+  }
+}

lib/widgets/priority_settings_scaffold.dart

@@ -1,7 +1,7 @@
 import 'package:flutter/material.dart';
 import 'package:spotiflac_android/l10n/l10n.dart';
 import 'package:spotiflac_android/utils/adaptive_layout.dart';
-import 'package:spotiflac_android/widgets/settings_sliver_app_bar.dart';
+import 'package:spotiflac_android/widgets/app_sliver_header.dart';
 
 class PrioritySettingsScaffold extends StatelessWidget {
   final bool hasChanges;
@@ -55,7 +55,7 @@ class PrioritySettingsScaffold extends StatelessWidget {
       child: Scaffold(
         body: CustomScrollView(
           slivers: [
-            SettingsSliverAppBar(
+            AppSliverHeader.page(
               title: title,
               leading: IconButton(
                 tooltip: MaterialLocalizations.of(context).backButtonTooltip,

lib/widgets/settings_sliver_app_bar.dart

@@ -1,64 +0,0 @@
-import 'package:flutter/material.dart';
-import 'package:spotiflac_android/utils/app_bar_layout.dart';
-
-/// The collapsing header shared by settings-style pages: a pinned
-/// [SliverAppBar] whose title slides toward the leading edge and shrinks
-/// from 28 to 20 logical pixels as the header collapses.
-class SettingsSliverAppBar extends StatelessWidget {
-  const SettingsSliverAppBar({
-    super.key,
-    required this.title,
-    this.actions,
-    this.leading,
-  });
-
-  final String title;
-  final List<Widget>? actions;
-
-  /// Defaults to a back button popping the current route.
-  final Widget? leading;
-
-  @override
-  Widget build(BuildContext context) {
-    final colorScheme = Theme.of(context).colorScheme;
-    final topPadding = normalizedHeaderTopPadding(context);
-    return SliverAppBar(
-      expandedHeight: 120 + topPadding,
-      collapsedHeight: kToolbarHeight,
-      floating: false,
-      pinned: true,
-      backgroundColor: colorScheme.surface,
-      surfaceTintColor: Colors.transparent,
-      leading:
-          leading ??
-          IconButton(
-            tooltip: MaterialLocalizations.of(context).backButtonTooltip,
-            icon: const Icon(Icons.arrow_back),
-            onPressed: () => Navigator.pop(context),
-          ),
-      actions: actions,
-      flexibleSpace: LayoutBuilder(
-        builder: (context, constraints) {
-          final maxHeight = 120 + topPadding;
-          final minHeight = kToolbarHeight + topPadding;
-          final expandRatio =
-              ((constraints.maxHeight - minHeight) / (maxHeight - minHeight))
-                  .clamp(0.0, 1.0);
-          final leftPadding = 56 - (32 * expandRatio);
-          return FlexibleSpaceBar(
-            expandedTitleScale: 1.0,
-            titlePadding: EdgeInsets.only(left: leftPadding, bottom: 16),
-            title: Text(
-              title,
-              style: TextStyle(
-                fontSize: 20 + (8 * expandRatio),
-                fontWeight: FontWeight.bold,
-                color: colorScheme.onSurface,
-              ),
-            ),
-          );
-        },
-      ),
-    );
-  }
-}