iOS push notification setup for client_app and mitra_app

- Add Runner.entitlements with aps-environment capability
- Add UIBackgroundModes (remote-notification, fetch) to Info.plist
- Add CODE_SIGN_ENTITLEMENTS to Debug/Release/Profile build configs
- Add GoogleService-Info.plist for both apps
- Upgrade Firebase packages and web_socket_channel to fix CocoaPods conflict
- Set client_app Podfile iOS platform to 15.0
- Fix mitra_app Xcode bundle ID to match Firebase (com.halobestie.mitra)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

client_app/ios/Flutter/AppFrameworkInfo.plist

@@ -20,7 +20,5 @@
   <string>????</string>
   <key>CFBundleVersion</key>
   <string>1.0</string>
-  <key>MinimumOSVersion</key>
-  <string>13.0</string>
 </dict>
 </plist>