feat(mobile-next): 导入官方 openim-flutter-demo 固定基线 3.8.3-patch.3 并完成双构建

- 上游: github.com/OpenIMSDK/openim-flutter-demo tag 3.8.3-patch.3
  commit b3dfdb1e8aaeaaf6f0793e10cadd20d5c184a31f
- 并行目录 mobile-next/ 原样导入（含 LICENSE），不覆盖现网 mobile/
- 锁定 Flutter 3.24.5 / Dart 3.5.4 / JDK 17 / Gradle 7.6.3 / AGP 7.3.1
- 实测 Android debug 与 release 构建均成功（见 docs/mobile-next-baseline-import.md）
- 本提交可单独回退：git revert 1db1229（重写前）

Co-authored-by: multica-agent <github@multica.ai>

mobile-next/ios/Runner/GoogleService-Info.plist

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>API_KEY</key>
+	<string>AIzaSyC0BhV-mo84LvOuqWf2bS966jlf0f8mh74</string>
+	<key>GCM_SENDER_ID</key>
+	<string>299075855003</string>
+	<key>PLIST_VERSION</key>
+	<string>1</string>
+	<key>BUNDLE_ID</key>
+	<string>io.openim.flutter.base</string>
+	<key>PROJECT_ID</key>
+	<string>im-fer-c3347</string>
+	<key>STORAGE_BUCKET</key>
+	<string>im-fer-c3347.firebasestorage.app</string>
+	<key>IS_ADS_ENABLED</key>
+	<false></false>
+	<key>IS_ANALYTICS_ENABLED</key>
+	<false></false>
+	<key>IS_APPINVITE_ENABLED</key>
+	<true></true>
+	<key>IS_GCM_ENABLED</key>
+	<true></true>
+	<key>IS_SIGNIN_ENABLED</key>
+	<true></true>
+	<key>GOOGLE_APP_ID</key>
+	<string>1:299075855003:ios:23b06300e33d984309dc3e</string>
+</dict>
+</plist>