Arcane: Missing admin authorization on global variables endpoint

Arcane is an interface for managing Docker containers, images, networks, and volumes. Prior to 1.19.2, the PUT /api/environments/{id}/templates/variables endpoint, which writes the system-wide .env.global file used for variable substitution in every project's compose file, is missing an admin authorization check. Any authenticated non-admin user can call this endpoint with their bearer token or API key and overwrite the global environment variables that are merged into every project deployment. By overriding values like REGISTRY, IMAGE, DATABASE_URL, or SECRET_KEY that other users reference via ${VAR} in compose files, an attacker can redirect image pulls to attacker-controlled registries (supply-chain RCE on the Docker host), exfiltrate database credentials, or disrupt all projects. This vulnerability is fixed in 1.19.2.