Implement iOS settings/preferences store

- Created Settings directory with core store files
- Implemented SettingsStore with UserDefaults/App Group support
- Created AppSettings for app-wide configuration
- Created UserPreferences for unified preferences access
- Added enableAll/disableAll methods to ReadingPreferences
- Added enableAll/disableAll methods to NotificationPreferences
- Created SettingsMigration framework for version migrations

This implements the core settings infrastructure for iOS.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

native-route/linux/gsettings/org.rssuper.notification.preferences.gschema.xml

@@ -0,0 +1,74 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gsettings schema="org.rssuper.notification.preferences">
+    <prefix>rssuper</prefix>
+    <binding>
+        <property name="newArticles" type="boolean"/>
+    </binding>
+    <binding>
+        <property name="episodeReleases" type="boolean"/>
+    </binding>
+    <binding>
+        <property name="customAlerts" type="boolean"/>
+    </binding>
+    <binding>
+        <property name="badgeCount" type="boolean"/>
+    </binding>
+    <binding>
+        <property name="sound" type="boolean"/>
+    </binding>
+    <binding>
+        <property name="vibration" type="boolean"/>
+    </binding>
+    <binding>
+        <property name="preferences" type="json"/>
+    </binding>
+    
+    <keyvalue>
+        <key name="newArticles">New Article Notifications</key>
+        <default>true</default>
+        <description>Enable notifications for new articles</description>
+    </keyvalue>
+    
+    <keyvalue>
+        <key name="episodeReleases">Episode Release Notifications</key>
+        <default>true</default>
+        <description>Enable notifications for episode releases</description>
+    </keyvalue>
+    
+    <keyvalue>
+        <key name="customAlerts">Custom Alert Notifications</key>
+        <default>true</default>
+        <description>Enable notifications for custom alerts</description>
+    </keyvalue>
+    
+    <keyvalue>
+        <key name="badgeCount">Badge Count</key>
+        <default>true</default>
+        <description>Show badge count in app header</description>
+    </keyvalue>
+    
+    <keyvalue>
+        <key name="sound">Sound</key>
+        <default>true</default>
+        <description>Play sound on notification</description>
+    </keyvalue>
+    
+    <keyvalue>
+        <key name="vibration">Vibration</key>
+        <default>true</default>
+        <description>Vibrate device on notification</description>
+    </keyvalue>
+    
+    <keyvalue>
+        <key name="preferences">All Preferences</key>
+        <default>{
+            "newArticles": true,
+            "episodeReleases": true,
+            "customAlerts": true,
+            "badgeCount": true,
+            "sound": true,
+            "vibration": true
+        }</default>
+        <description>All notification preferences as JSON</description>
+    </keyvalue>
+</gsettings>