fix(mobile): use fastlane setup_ci for keychain management (official approach)

mobile/ios/fastlane/Fastfile

@@ -48,21 +48,16 @@ platform :ios do
   
   # Helper method to sync certificates and profiles using match
   def sync_code_signing(app_identifiers:, readonly: true)
-    keychain = ENV["KEYCHAIN_NAME"] || "login.keychain"
-    keychain_password = ENV["KEYCHAIN_PASSWORD"] || ""
+    # Use fastlane's setup_ci which creates a temporary keychain and handles everything
+    if ENV["CI"]
+      setup_ci
+    end
     
     match(
       type: "appstore",
       app_identifier: app_identifiers,
-      readonly: readonly,
-      keychain_name: keychain,
-      keychain_password: keychain_password
+      readonly: readonly
     )
-    
-    # Set key partition list after match imports certificates (required for CI)
-    if ENV["CI"] && !keychain_password.empty?
-      sh("security set-key-partition-list -S apple-tool:,apple: -s -k \"#{keychain_password}\" #{keychain} 2>/dev/null || true")
-    end
   end
   
   # Helper method to get version from pubspec.yaml