Adapt deployment for Dokploy

Replace the Gitea Actions SSH deploy with a Docker image
(serversideup/php fpm-nginx) and docker-compose setup. Store the
SQLite database inside the persistent storage volume, trust the
reverse proxy, and move admin credentials into config so they work
with cached configuration.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.env.example

@@ -64,6 +64,9 @@ AWS_USE_PATH_STYLE_ENDPOINT=false
 
 VITE_APP_NAME="${APP_NAME}"
 
+ADMIN_USER=admin
+ADMIN_PASS=change-me
+
 FILE_LINKS_ENABLED=false
 FILE_LINKS_DISK=local
 FILE_LINKS_DIRECTORY=temporary-links