Record renderer attachment when L1 verifies token

When L1 successfully calls /auth/verify, the user's attachment to
that L1 server is recorded in the user_renderers table.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server.py

@@ -1332,6 +1332,9 @@ async def verify_auth(
     if not username:
         raise HTTPException(401, "Invalid token")
 
+    # Record the attachment (L1 successfully verified user's token)
+    await db.attach_renderer(username, l1_normalized)
+
     return {"username": username, "valid": True, "l1_server": request.l1_server}