docs(readme): add non-affiliation note (per upstream opencode request)

The upstream opencode project asks 'opencode-*' named projects to clarify they are
not built by or affiliated with the opencode team. Adds that note near the top.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -8,6 +8,10 @@ AI-assisted coding from your phone — Android, via F-Droid or a direct APK.
 [![Download APK](https://img.shields.io/badge/Download-APK-green?logo=android)](https://github.com/dzianisv/opencode-mobile/releases/latest)
 [![Google Play](https://img.shields.io/badge/Google_Play-coming_soon-lightgrey?logo=google-play)](#)
 
+> **Not affiliated with opencode.** OpenCode Mobile is an independent, community-built client and is
+> not made by, endorsed by, or affiliated with the opencode / Anomaly team. It talks to an opencode
+> server you run yourself, using opencode's open HTTP API.
+
 ---
 
 ## Install (Android)