Update docker-compose files to use configurable environment variables

- Replace hardcoded paths with variables: STACKS_DIR, PROJECTS_DIR, MEDIA_DIR, DOWNLOAD_DIR
- Update .env.example with new variable definitions
- Remove unused .template files
- Enable configurable directory paths for stacks, media, and downloads

docker-compose/dashboards/docker-compose.yml

@@ -28,7 +28,7 @@ services:
     volumes:
       - ./homepage:/app/config
       - /var/run/docker.sock:/var/run/docker.sock # For Docker integration do not mount RO
-      - /opt/stacks:/opt/stacks # To discover other stacks
+      - ${STACKS_DIR}:${STACKS_DIR} # To discover other stacks
     environment:
       - PUID=${PUID}  # Must be set to the docker user ID
       - PGID=${PGID}  # Must be set to the docker group ID
@@ -83,7 +83,7 @@ services:
       - ./homarr/icons:/app/public/icons
       - /var/run/docker.sock:/var/run/docker.sock
     environment:
-      - TZ=America/New_York
+      - TZ=${TZ}
       - SECRET_ENCRYPTION_KEY=8830c9434b05ebfe3e31340c685fea63446ab3f635c4fad68370006949ed30df
     healthcheck:
       test: ['CMD', 'curl', '-f', 'http://localhost:7575/']