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>

trilium/docker-compose.yml

@@ -10,7 +10,7 @@ services:
       TZ: ${TZ}
 
     volumes:
-      - ${TRILIUM_DATA_PATH}:/home/node/trilium-data:Z
+      - /opt/trilium/data:/home/node/trilium-data:Z
 
     expose:
       - "${TRILIUM_HTTP_PORT}"