Vendor push SDKs

Place the official Huawei, Honor, Xiaomi, OPPO/Heytap, vivo and Meizu Android SDK AAR/JAR files in this directory during CI or a local release build. Binary SDK files are intentionally ignored by git. Public client app IDs and app keys are injected through the PUSH_* Gradle properties or environment variables; provider master secrets belong only on the API server.