Docker, Docker-AIO: one .env example per compose file

Replace each folder's shared .env.example with one example per compose
file, named after it (docker-compose.<name>.yml takes
.env.<name>.example), as DriverVault does. Each lists only the settings
its compose file uses, names the required ones in its header, and the
prod examples start from a public server name. Every variable a compose
file substitutes is defined in its example.

The compose headers point at their own example. The SeaweedFS files now
fix WARP_PB_S3_REGION at us-east-1 instead of reading it from .env,
since SeaweedFS ignores the region.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Docker-AIO/docker-compose.postgresql.prod.yml

@@ -2,7 +2,7 @@
 # client and PostgreSQL in one container, pulled from a registry.
 #
 #   cd Docker-AIO
-#   cp .env.example .env      # then edit it
+#   cp .env.postgresql.prod.example .env      # then edit it
 #   docker compose -f docker-compose.postgresql.prod.yml up -d
 #
 # PostgreSQL runs inside the container, listening only on a Unix socket