add pixelfed to mastodon DM compatible

backend/src/lib/delivery/mastodon.ts

@@ -44,7 +44,8 @@ class MastodonCompatible_ extends DeliveryProvider<{ token: string }> {
 
   isThisFor(software_name: string): boolean {
     // TODO: add other softwares that work w/ mastodon DMs
-    return software_name === "mastodon";
+    const compatible = ["mastodon", "pixelfed"];
+    return compatible.indexOf(software_name) > -1;
   }
 
   async send(