fix: replace variable bind mounts with hardcoded paths/named volumes

Coolify converts ${VAR}:/path bind mounts to named Docker volumes when
the variable is not resolved. Fixed per stack:

- adguard: -> named volumes (data already in Coolify-created volumes)
- authentik: -> named volumes (data already in Coolify-created volumes)
- gitea: -> /opt/gitea/{postgres,data,runner}
- mail-relay: -> /opt/mail-relay/{queue,opendkim,secrets/...}
- media-server: COMMON_PATH -> /opt/media (hardcoded)
- trilium: -> /opt/trilium/data
- wireguard: -> /opt/wg-easy + /lib/modules

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

mail-relay/docker-compose.yml

@@ -31,9 +31,9 @@ services:
       DKIM_SELECTOR: ${MAIL_RELAY_DKIM_SELECTOR}
 
     volumes:
-      - ${MAIL_RELAY_QUEUE_PATH}:/var/spool/postfix:Z
-      - ${MAIL_RELAY_DKIM_KEYS_PATH}:/etc/opendkim/keys:Z
-      - ${MAIL_RELAY_PASSWORD_FILE_PATH}:/run/secrets/relayhost_password:ro,Z
+      - /opt/mail-relay/queue:/var/spool/postfix:Z
+      - /opt/mail-relay/opendkim:/etc/opendkim/keys:Z
+      - /opt/mail-relay/secrets/relayhost_password:/run/secrets/relayhost_password:ro,Z
 
     networks:
       mail_internal: