feat(mobile): sync themes per community

mobile/lib/app.dart

@@ -50,9 +50,13 @@ class App extends HookConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final themeMode = ref.watch(themeProvider);
-    final accentIndex = ref.watch(accentProvider);
-    final schemeName = ref.watch(schemeProvider);
+    final communityTheme = ref.watch(communityThemeProvider);
+    final themeMode = communityTheme.mode;
+    final accentIndex = effectiveAccentIndex(
+      communityTheme.theme,
+      communityTheme.accent,
+    );
+    final schemeName = communityTheme.theme;
     final authState = ref.watch(authProvider);
 
     final resolved = resolveSchemes(schemeName, themeMode);

mobile/lib/features/settings/accent_picker_page.dart

@@ -15,7 +15,9 @@ class AccentPickerPage extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final selected = ref.watch(accentProvider);
+    final selected =
+        accentIndexForWireValue(ref.watch(communityThemeProvider).accent) ??
+        defaultAccentIndex;
     final colorScheme = context.colors;
 
     return FrostedScaffold(
@@ -31,7 +33,8 @@ class AccentPickerPage extends ConsumerWidget {
               color: accentColorForScheme(colorScheme, i),
               label: accentColors[i].name,
               selected: selected == i,
-              onTap: () => ref.read(accentProvider.notifier).setAccent(i),
+              onTap: () =>
+                  ref.read(communityThemeProvider.notifier).setAccent(i),
             ),
         ],
       ),

mobile/lib/features/settings/settings_page/appearance_section.dart

@@ -15,12 +15,16 @@ class _AppearanceSection extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final mode = ref.watch(themeProvider);
-    final schemeName = ref.watch(schemeProvider);
-    final accentIndex = ref.watch(accentProvider);
+    final preference = ref.watch(communityThemeProvider);
+    final mode = preference.mode;
+    final schemeName = preference.theme;
+    final accentIndex = effectiveAccentIndex(
+      preference.theme,
+      preference.accent,
+    );
 
     return AppListCard(
-      label: 'Style',
+      label: 'Style · This community',
       children: [
         AppListRow(
           icon: LucideIcons.sunMoon,
@@ -38,16 +42,17 @@ class _AppearanceSection extends ConsumerWidget {
             MaterialPageRoute<void>(builder: (_) => const ThemePickerPage()),
           ),
         ),
-        AppListRow(
-          icon: LucideIcons.droplet,
-          title: 'Accent color',
-          // The swatch *is* the value — naming the color as well would say the
-          // same thing twice, so it takes the chevron's place.
-          trailing: _AccentSwatch(accentIndex: accentIndex),
-          onTap: () => Navigator.of(context).push(
-            MaterialPageRoute<void>(builder: (_) => const AccentPickerPage()),
+        if (!isBuzzTheme(effectiveTheme(schemeName, mode)?.name ?? schemeName))
+          AppListRow(
+            icon: LucideIcons.droplet,
+            title: 'Accent color',
+            // The swatch *is* the value — naming the color as well would say the
+            // same thing twice, so it takes the chevron's place.
+            trailing: _AccentSwatch(accentIndex: accentIndex),
+            onTap: () => Navigator.of(context).push(
+              MaterialPageRoute<void>(builder: (_) => const AccentPickerPage()),
+            ),
           ),
-        ),
       ],
     );
   }
@@ -68,7 +73,7 @@ class _AppearanceModeSheet extends ConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final mode = ref.watch(themeProvider);
+    final mode = ref.watch(communityThemeProvider).mode;
 
     return SafeArea(
       child: Column(
@@ -96,15 +101,7 @@ class _AppearanceModeSheet extends ConsumerWidget {
                     )
                   : null,
               onTap: () {
-                final schemeName = ref.read(schemeProvider);
-                final compatibleScheme = schemeForAppearanceMode(
-                  schemeName,
-                  option.mode,
-                );
-                if (compatibleScheme != schemeName) {
-                  ref.read(schemeProvider.notifier).setScheme(compatibleScheme);
-                }
-                ref.read(themeProvider.notifier).setMode(option.mode);
+                ref.read(communityThemeProvider.notifier).setMode(option.mode);
                 Navigator.of(context).pop();
               },
             ),

mobile/lib/features/settings/theme_picker_page.dart

@@ -18,8 +18,9 @@ class ThemePickerPage extends HookConsumerWidget {
 
   @override
   Widget build(BuildContext context, WidgetRef ref) {
-    final mode = ref.watch(themeProvider);
-    final selectedScheme = ref.watch(schemeProvider);
+    final preference = ref.watch(communityThemeProvider);
+    final mode = preference.mode;
+    final selectedScheme = preference.theme;
     final searchQuery = useState('');
     final searchController = useTextEditingController();
     final scrollController = useScrollController();
@@ -112,8 +113,8 @@ class ThemePickerPage extends HookConsumerWidget {
                         label: labelFor(theme),
                         selected: isSelected(theme),
                         onTap: () => ref
-                            .read(schemeProvider.notifier)
-                            .setScheme(theme.name),
+                            .read(communityThemeProvider.notifier)
+                            .setTheme(theme.name),
                       );
                     },
                   ),

mobile/lib/shared/theme/accent_colors.dart

@@ -6,41 +6,78 @@ class AccentColor {
   final Color light;
   final Color dark;
   final bool useThemeForegroundInDark;
+  final String wireValue;
 
   const AccentColor({
     required this.name,
     required this.light,
     required this.dark,
     this.useThemeForegroundInDark = false,
+    required this.wireValue,
   });
 }
 
 const accentColors = [
-  AccentColor(name: 'Blue', light: Color(0xFF3B82F6), dark: Color(0xFF60A5FA)),
-  AccentColor(name: 'Cyan', light: Color(0xFF06B6D4), dark: Color(0xFF22D3EE)),
-  AccentColor(name: 'Green', light: Color(0xFF22C55E), dark: Color(0xFF4ADE80)),
+  AccentColor(
+    name: 'Neutral',
+    light: Color(0xFF000000),
+    dark: Color(0xFFE1E4E8),
+    wireValue: 'neutral',
+    useThemeForegroundInDark: true,
+  ),
+  AccentColor(
+    name: 'Blue',
+    light: Color(0xFF3B82F6),
+    dark: Color(0xFF60A5FA),
+    wireValue: '#3b82f6',
+  ),
+  AccentColor(
+    name: 'Cyan',
+    light: Color(0xFF06B6D4),
+    dark: Color(0xFF22D3EE),
+    wireValue: '#06b6d4',
+  ),
+  AccentColor(
+    name: 'Green',
+    light: Color(0xFF22C55E),
+    dark: Color(0xFF4ADE80),
+    wireValue: '#22c55e',
+  ),
   AccentColor(
     name: 'Orange',
     light: Color(0xFFF97316),
     dark: Color(0xFFFB923C),
+    wireValue: '#f97316',
+  ),
+  AccentColor(
+    name: 'Red',
+    light: Color(0xFFEF4444),
+    dark: Color(0xFFF87171),
+    wireValue: '#ef4444',
+  ),
+  AccentColor(
+    name: 'Pink',
+    light: Color(0xFFEC4899),
+    dark: Color(0xFFF472B6),
+    wireValue: '#ec4899',
+  ),
+  AccentColor(
+    name: 'Lilac',
+    light: Color(0xFFC0A2F1),
+    dark: Color(0xFFC0A2F1),
+    wireValue: '#c0a2f1',
   ),
-  AccentColor(name: 'Red', light: Color(0xFFEF4444), dark: Color(0xFFF87171)),
-  AccentColor(name: 'Pink', light: Color(0xFFEC4899), dark: Color(0xFFF472B6)),
   AccentColor(
     name: 'Purple',
     light: Color(0xFFA855F7),
     dark: Color(0xFFC084FC),
+    wireValue: '#a855f7',
   ),
   AccentColor(
     name: 'Indigo',
     light: Color(0xFF6366F1),
     dark: Color(0xFF818CF8),
-  ),
-  AccentColor(
-    name: 'Black',
-    light: Color(0xFF000000),
-    dark: Color(0xFFFFFFFF),
-    useThemeForegroundInDark: true,
+    wireValue: '#6366f1',
   ),
 ];
 
@@ -59,7 +96,26 @@ Color accentColorForScheme(ColorScheme scheme, int accentIndex) {
 ///
 /// Keep this at the end of [accentColors] so existing saved accent indexes keep
 /// pointing at the same colors.
-const defaultAccentIndex = 8;
+const neutralAccentIndex = 0;
+const defaultAccentIndex = neutralAccentIndex;
 
 /// Legacy default: Catppuccin Mauve/the base theme primary.
 const legacyDefaultAccentIndex = -1;
+
+int? accentIndexForWireValue(String value) {
+  final index = accentColors.indexWhere((accent) => accent.wireValue == value);
+  return index < 0 ? null : index;
+}
+
+String legacyAccentWireValue(int? index) {
+  // Legacy mobile indexes 0...7 match desktop Blue...Indigo except Lilac,
+  // which did not exist. Black (8) has no desktop wire value, so migrate it
+  // deterministically to Neutral rather than publishing a mobile-only value.
+  if (index == 8) return 'neutral';
+  if (index != null && index >= 0 && index <= 5) {
+    return accentColors[index + 1].wireValue;
+  }
+  if (index == 6) return '#a855f7';
+  if (index == 7) return '#6366f1';
+  return '#3b82f6';
+}

mobile/lib/shared/theme/buzz_theme.dart

@@ -1,5 +1,7 @@
 import 'package:flutter/material.dart';
 
+import 'accent_colors.dart';
+
 /// Name of the first-party Buzz theme. Buzz reuses the GitHub Light palette for
 /// every base color; the one thing that sets it apart is a branded gradient
 /// painted across the app's top section. Mirrors desktop, where the same
@@ -17,6 +19,13 @@ const buzzDarkThemeName = 'buzz-dark';
 bool isBuzzTheme(String themeName) =>
     themeName == buzzThemeName || themeName == buzzDarkThemeName;
 
+/// Buzz renders with its fixed neutral foreground while preserving the stored
+/// wire accent so the user's choice returns on another theme.
+int effectiveAccentIndex(String themeName, String storedAccent) {
+  if (isBuzzTheme(themeName)) return neutralAccentIndex;
+  return accentIndexForWireValue(storedAccent) ?? defaultAccentIndex;
+}
+
 /// Gradient stops, matching desktop's `--buzz-gradient-*` custom properties.
 const _lightTop = Color(0xFFE6E6B6);
 const _lightBottom = Color(0xFFC4D0DA);