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>

gitea/docker-compose.yml

@@ -9,7 +9,7 @@ services:
       POSTGRES_PASSWORD: ${GITEA_DB_PASSWORD}
       TZ: ${TZ}
     volumes:
-      - ${GITEA_POSTGRES_PATH}:/var/lib/postgresql/data:Z
+      - /opt/gitea/postgres:/var/lib/postgresql/data:Z
     networks:
       - gitea
 
@@ -62,7 +62,7 @@ services:
       GITEA__ui__THEMES: ${GITEA_UI_THEMES}
 
     volumes:
-      - ${GITEA_DATA_PATH}:/data:Z
+      - /opt/gitea/data:/data:Z
     networks:
       - gitea
       - proxy
@@ -83,7 +83,7 @@ services:
       GITEA_RUNNER_NAME: ${GITEA_RUNNER_NAME}
       GITEA_RUNNER_LABELS: ${GITEA_RUNNER_LABELS}
     volumes:
-      - ${GITEA_RUNNER_DATA_PATH}:/data:Z
+      - /opt/gitea/runner:/data:Z
       - /var/run/docker.sock:/var/run/docker.sock:Z
     networks:
       - gitea