chore(images): pin service image updates

Replace floating service images with reviewable tags or digests.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

vaultwarden/compose.yaml

@@ -1,7 +1,7 @@
 services:
   server:
     container_name: vaultwarden-server
-    image: vaultwarden/server:latest
+    image: vaultwarden/server:1.37.3
     restart: unless-stopped
     ports:
       - 9993:80