fix(dankserver): copyparty volume root via COPAY_VOL

The ac edition maps volumes from COPAY_* envs; without a volume root every
request resolves zero volumes and the app answers HTTP 500 with its own error
page. Point it at /w where the LUKS array is mounted.

dankserver/compose.yaml

@@ -78,6 +78,7 @@ services:
     container_name: copyparty
     restart: unless-stopped
     environment:
+      COPAY_VOL: "/w"
       COPAY_PASS: "${COPAY_PASS}"
       COPAY_MODE: rw
     ports: