Standardize .env.example files with complete variables and empty values

Changes:
- Reviewed all docker-compose files to identify required variables
- Updated all .env.example files to include ONLY variables used in their respective compose files
- Changed all placeholder values to empty strings for cleaner configuration
- Fixed variable name inconsistency: DOWNLOADS_DIR -> DOWNLOAD_DIR (to match main .env)
- Removed unnecessary variables that aren't used by the compose files

All .env.example files now:
- Contain only the variables actually used in the stack
- Have empty values instead of example placeholders
- Match the variable names used in docker-compose files

This ensures clean, minimal .env files for each stack without any extraneous variables or confusing placeholder values.

docker-compose/media-management/docker-compose.yml

@@ -18,7 +18,7 @@ services:
     volumes:
       - ./sonarr/config:/config
       - ${MEDIA_DIR}:/media
-      - ${DOWNLOADS_DIR}:/downloads # Large downloads on separate drive
+      - ${DOWNLOAD_DIR}:/downloads # Large downloads on separate drive
     environment:
       - PUID=${PUID}
       - PGID=${PUID}
@@ -63,7 +63,7 @@ services:
     volumes:
       - ./radarr/config:/config
       - ${MEDIA_DIR}:/media
-      - ${DOWNLOADS_DIR}:/downloads # Large downloads on separate drive
+      - ${DOWNLOAD_DIR}:/downloads # Large downloads on separate drive
     environment:
       - PUID=${PUID}
       - PGID=${PUID}
@@ -152,7 +152,7 @@ services:
     volumes:
       - ./readarr/config:/config
       - ${MEDIA_DIR}/books:/books
-      - ${DOWNLOADS_DIR}:/downloads
+      - ${DOWNLOAD_DIR}:/downloads
     environment:
       - PUID=${PUID}
       - PGID=${PUID}
@@ -191,7 +191,7 @@ services:
     volumes:
       - ./lidarr/config:/config
       - ${MEDIA_DIR}/music:/music
-      - ${DOWNLOADS_DIR}:/downloads
+      - ${DOWNLOAD_DIR}:/downloads
     environment:
       - PUID=${PUID}
       - PGID=${PUID}
@@ -230,7 +230,7 @@ services:
     volumes:
       - ./lazylibrarian/config:/config
       - ${MEDIA_DIR}/books:/books
-      - ${DOWNLOADS_DIR}:/downloads
+      - ${DOWNLOAD_DIR}:/downloads
     environment:
       - PUID=${PUID}
       - PGID=${PUID}
@@ -270,7 +270,7 @@ services:
     volumes:
       - ./mylar3/config:/config
       - ${MEDIA_DIR}/comics:/comics
-      - ${DOWNLOADS_DIR}:/downloads
+      - ${DOWNLOAD_DIR}:/downloads
     environment:
       - PUID=${PUID}
       - PGID=${PUID}