ci: build tracker image for linux/arm64 (Pi host)

Desktop runner is amd64; the Pi deploy target needs arm64 images.

Co-authored-by: Cursor <cursoragent@cursor.com>

.drone.yml

@@ -59,6 +59,7 @@ steps:
     settings:
       repo: registry.zea.lt/miczek/tracker
       registry: registry.zea.lt
+      platform: linux/arm64
       username:
         from_secret: registry_username
       password: