fix(antigravity): 🐛 add platform/architecture to User-Agent header

The User-Agent header was previously only including the antigravity version number. This update appends platform and architecture information (windows/amd64) to improve server-side request tracking and debugging capabilities.

Author: Mirrowel

src/rotator_library/providers/antigravity_provider.py

@@ -3225,7 +3225,7 @@ async def acompletion(
             "Authorization": f"Bearer {token}",
             "Content-Type": "application/json",
             "Host": host,
-            "User-Agent": "antigravity/1.11.9",
+            "User-Agent": "antigravity/1.11.9 windows/amd64",
             "Accept": "text/event-stream" if stream else "application/json",
         }