feat(caddy): single owner via CADDY_MANAGER env flag

One Caddy serves the whole container and POST /load replaces the entire
config, so two instances pushing would clobber each other. Now only the
instance with CADDY_MANAGER=true (production) pushes, seeds routes from the
Caddyfile, and accepts route mutations (others get 403). /api/auth/config
exposes caddyManaged so the non-owner Settings UI shows the Caddy section
read-only. The installer sets the flag on the production .env only.

deploy/proxmox-ghostgrid.sh

@@ -190,6 +190,8 @@ msg_info "Creating .env file for each instance"
 for d in "${APP_DIR}" "${DEV_DIR}"; do
   SECRET="$(openssl rand -hex 32)"
   run "printf 'JWT_SECRET=\"%s\"\n' '${SECRET}' > ${d}/.env && chown ghostgrid:ghostgrid ${d}/.env && chmod 600 ${d}/.env"
+  # Only the production instance owns the shared Caddy (one Caddy per container).
+  [[ "$d" == "${APP_DIR}" ]] && run "printf 'CADDY_MANAGER=true\n' >> ${d}/.env"
 done
 msg_ok ".env files created (main + dev)"