feat(storage-kit): implement SettingsStore for app settings management

[husamettinarabaci]

Is your feature request related to a problem?

The SettingsStore skeleton class exists in packages/storage_kit/lib/settings/settings_store.dart but needs full implementation to provide a high-level API for app settings management with reactive updates, type-safe access, and default values.

Describe the solution you'd like

Implement a fully functional SettingsStore service that manages app settings using KeyValueStore, provides reactive streams for setting changes, type-safe accessors, default values, and validation.

What is SettingsStore and why do we need it?

SettingsStore is a high-level service for managing app settings with type-safe access, default values, change notifications, and validation, built on top of KeyValueStore.

Why it's important:

• Type Safety: Strongly-typed settings instead of string keys
• Defaults: Automatic fallback to default values
• Reactive: Widgets rebuild when settings change
• Validation: Ensures valid setting values
• Centralized: All app settings in one place

Common use cases:

• Theme mode setting (light/dark/system)
• Language/locale preference
• Notification preferences
• Privacy settings
• Accessibility settings
• Feature toggles

Required Deliverables

1. SettingsStore implementation with:

   • Theme mode getter/setter
   • Locale preference getter/setter
   • Notification enabled getter/setter
   • Custom settings getter/setter
   • Default values
   • Settings change stream
   • Reset to defaults method
   • Integration with KeyValueStore
   • Type-safe API

2. Widgetbook stories (6-8 use cases):

   • Get theme mode setting
   • Set theme mode setting
   • Get locale setting
   • Set notification preference
   • Settings change stream
   • Reset to defaults
   • Custom settings
   • Settings inspector UI

3. SPDX headers in all source files

Key Implementation Specs

• Use KeyValueStore for persistence
• ThemeMode get themeMode
• Future setThemeMode(ThemeMode)
• Locale get locale
• Future setLocale(Locale)
• bool get notificationsEnabled
• Future setNotificationsEnabled(bool)
• Stream settingsStream
• resetToDefaults() method
• Default values as static const
• Singleton pattern recommended

Acceptance Criteria

• SettingsStore class implemented
• themeMode getter/setter
• locale getter/setter
• notificationsEnabled getter/setter
• Custom settings support
• Default values defined
• settingsStream emits changes
• resetToDefaults() works
• Integration with KeyValueStore
• Type-safe API
• Validation on setters
• All 6-8 Widgetbook stories created and functional
• SPDX headers present in all files
• Code follows STYLE_GUIDE.md standards
• Unit tests cover settings operations

Related Files

• packages/storage_kit/lib/settings/settings_store.dart (skeleton)
• packages/storage_kit/lib/key_value/key_value_store.dart (storage backend)
• widgetbook_kit/lib/stories/storage_kit/settings_store_story.dart (Widgetbook)

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Impact: Centralizes app settings; improves settings management UX

Priority: High