fix: 임시 키체인을 기본 키체인으로 설정 + readonly 복원

- default_keychain: true 추가 (export 시 인증서 검색 보장)
- readonly: true 복원 (Apple Portal 접근 불필요)
- verbose: true 유지 (디버깅용)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: boring-km

ios/fastlane/Fastfile

@@ -14,6 +14,7 @@ def create_temp_keychain(name, password)
   create_keychain(
     name: name,
     password: password,
+    default_keychain: true,
     unlock: true,
     timeout: 0,
     lock_when_sleeps: false
@@ -32,6 +33,7 @@ platform :ios do
       type: 'appstore',
       app_identifier: ["#{BUNDLE_IDENTIFIER}", "#{EXTENSION_IDENTIFIER}"],
       git_basic_authorization: Base64.strict_encode64(ENV["GIT_AUTHORIZATION"]),
+      readonly: true,
       keychain_name: keychain_name,
       keychain_password: keychain_password,
       verbose: true