feat: Flexion channel build fixes

- Add google-services.json per-channel copy in SwitchChannel (Flexion has extra client)
- Add GooglePlay default google-services.json for fallback
- Switch Bundle Identifier per channel (Flexion → com.arkgame.ft.flexion)
- Fix FlexionSDKHelper missing BillingService import
- Fix Flexion AndroidManifest: add fullBackupContent override with flexion_backup_rules
- Add MainProcessName tools:replace to resolve gasdk/tuyoosdk manifest conflict
- Add billing:6.0.1 dependency for tuyoosdk AAR init compatibility

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

sdk-intergration/Assets/Plugins/Android/mainTemplate.gradle

@@ -72,7 +72,6 @@ dependencies {
     implementation 'com.appsflyer:purchase-connector:2.2.0' // Assets/AppsFlyer/Editor/AppsFlyerDependencies.xml:8
     implementation 'com.appsflyer:unity-wrapper:6.17.7' // Assets/AppsFlyer/Editor/AppsFlyerDependencies.xml:6
     implementation 'com.google.android.ump:user-messaging-platform:2.1.0' // Assets/MaxSdk/AppLovin/Editor/Dependencies.xml:5
-    implementation 'com.tapjoy:tapjoy-android-unitybridge:14.5.0' // Packages/com.unity.package-offerwall/Editor/TJPluginDependencies.xml:10
 // Android Resolver Dependencies End
 **DEPS**}