feat: implement dynamic theme palette selection

- Introduced a new feature allowing users to select from multiple accent color palettes for buttons, cards, and chat bubbles.
- Added `AppThemePalette` provider to manage the current theme palette and persist user selections.
- Updated the `AppTheme` class to utilize the selected palette for light and dark themes, enhancing visual customization.
- Enhanced the `AppCustomizationPage` to include a palette selector, improving user experience and personalization options.
- Updated localization files to support new palette selection UI elements in multiple languages.

lib/l10n/app_de.arb

@@ -260,6 +260,10 @@
   "followingSystem": "Dem System folgen: {theme}",
   "@followingSystem": {"placeholders": {"theme": {"type": "String"}}},
   "themeDark": "Dunkel",
+  "themePalette": "Farbpalette",
+  "@themePalette": {"description": "Titel für die Auswahl der App-Farbpalette."},
+  "themePaletteDescription": "Wählen Sie die Akzentfarben für Schaltflächen, Karten und Chatblasen.",
+  "@themePaletteDescription": {"description": "Hilfetext zur Erklärung der Palettenauswahl."},
   "themeLight": "Hell",
   "currentlyUsingDarkTheme": "Aktuell dunkles Thema",
   "currentlyUsingLightTheme": "Aktuell helles Thema",

lib/l10n/app_en.arb

@@ -519,6 +519,10 @@
   },
   "themeDark": "Dark",
   "@themeDark": {"description": "Theme label for dark appearance."},
+  "themePalette": "Accent palette",
+  "@themePalette": {"description": "Title for selecting the app color palette."},
+  "themePaletteDescription": "Choose the accent colors used for buttons, cards, and chat bubbles.",
+  "@themePaletteDescription": {"description": "Helper text explaining palette selection."},
   "themeLight": "Light",
   "@themeLight": {"description": "Theme label for light appearance."},
   "currentlyUsingDarkTheme": "Currently using Dark theme",

lib/l10n/app_fr.arb

@@ -260,6 +260,10 @@
   "followingSystem": "Selon le système : {theme}",
   "@followingSystem": {"placeholders": {"theme": {"type": "String"}}},
   "themeDark": "Sombre",
+  "themePalette": "Palette de couleurs",
+  "@themePalette": {"description": "Titre pour choisir la palette de couleurs de l'application."},
+  "themePaletteDescription": "Choisissez les couleurs d'accent utilisées pour les boutons, les cartes et les bulles de discussion.",
+  "@themePaletteDescription": {"description": "Texte d'aide expliquant la sélection de la palette."},
   "themeLight": "Clair",
   "currentlyUsingDarkTheme": "Thème sombre actuellement utilisé",
   "currentlyUsingLightTheme": "Thème clair actuellement utilisé",

lib/l10n/app_it.arb

@@ -260,6 +260,10 @@
   "followingSystem": "Segue il sistema: {theme}",
   "@followingSystem": {"placeholders": {"theme": {"type": "String"}}},
   "themeDark": "Scuro",
+  "themePalette": "Palette di colori",
+  "@themePalette": {"description": "Titolo per scegliere la palette di colori dell'app."},
+  "themePaletteDescription": "Scegli i colori di accento usati per pulsanti, schede e bolle di chat.",
+  "@themePaletteDescription": {"description": "Testo di supporto che spiega la scelta della palette."},
   "themeLight": "Chiaro",
   "currentlyUsingDarkTheme": "Attualmente tema scuro",
   "currentlyUsingLightTheme": "Attualmente tema chiaro",

lib/l10n/app_localizations.dart

@@ -1458,6 +1458,18 @@ abstract class AppLocalizations {
   /// **'Dark'**
   String get themeDark;
 
+  /// Title for selecting the app color palette.
+  ///
+  /// In en, this message translates to:
+  /// **'Accent palette'**
+  String get themePalette;
+
+  /// Helper text explaining palette selection.
+  ///
+  /// In en, this message translates to:
+  /// **'Choose the accent colors used for buttons, cards, and chat bubbles.'**
+  String get themePaletteDescription;
+
   /// Theme label for light appearance.
   ///
   /// In en, this message translates to:

lib/l10n/app_localizations_de.dart

@@ -755,6 +755,13 @@ class AppLocalizationsDe extends AppLocalizations {
   @override
   String get themeDark => 'Dunkel';
 
+  @override
+  String get themePalette => 'Farbpalette';
+
+  @override
+  String get themePaletteDescription =>
+      'Wählen Sie die Akzentfarben für Schaltflächen, Karten und Chatblasen.';
+
   @override
   String get themeLight => 'Hell';
 

lib/l10n/app_localizations_en.dart

@@ -751,6 +751,13 @@ class AppLocalizationsEn extends AppLocalizations {
   @override
   String get themeDark => 'Dark';
 
+  @override
+  String get themePalette => 'Accent palette';
+
+  @override
+  String get themePaletteDescription =>
+      'Choose the accent colors used for buttons, cards, and chat bubbles.';
+
   @override
   String get themeLight => 'Light';
 

lib/l10n/app_localizations_fr.dart

@@ -763,6 +763,13 @@ class AppLocalizationsFr extends AppLocalizations {
   @override
   String get themeDark => 'Sombre';
 
+  @override
+  String get themePalette => 'Palette de couleurs';
+
+  @override
+  String get themePaletteDescription =>
+      'Choisissez les couleurs d\'accent utilisées pour les boutons, les cartes et les bulles de discussion.';
+
   @override
   String get themeLight => 'Clair';
 

lib/l10n/app_localizations_it.dart

@@ -752,6 +752,13 @@ class AppLocalizationsIt extends AppLocalizations {
   @override
   String get themeDark => 'Scuro';
 
+  @override
+  String get themePalette => 'Palette di colori';
+
+  @override
+  String get themePaletteDescription =>
+      'Scegli i colori di accento usati per pulsanti, schede e bolle di chat.';
+
   @override
   String get themeLight => 'Chiaro';