Refactor Steam login callback to remove response struct and handle redirects directly

api/Authenticator.api

@@ -33,11 +33,7 @@ type (
 		OpenidSigned        string `form:"openid.signed"`
 		OpenidSig           string `form:"openid.sig"`
 	}
-	SteamLoginCallbackResp {
-		Success bool   `json:"success"`
-		SteamId string `json:"steamId,omitempty"`
-		Message string `json:"message,omitempty"`
-	}
+// No response needed - endpoint will redirect to frontend
 )
 
 @server (
@@ -60,9 +56,9 @@ service Authenticator {
 
 	@doc (
 		summary:     "Steam login callback"
-		description: "Handles the callback from Steam after user authentication"
+		description: "Validates Steam authentication and redirects to frontend with status"
 	)
 	@handler steamLoginCallbackHandler
-	get /steam/callback (SteamLoginCallbackReq) returns (SteamLoginCallbackResp)
+	get /steam/callback (SteamLoginCallbackReq)
 }