Docker: read every setting from a .env file

Each folder gets a .env.example listing every homeserver, admin panel
and web client setting with its default (empty means the default).
Compose reads .env for ports, registry and the PostgreSQL password, and
passes it to the containers through env_file; the compose files keep
only the database driver, connection string and internal addresses.
.env is git-ignored.

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

Docker/docker-compose.sqlite.prod.yml

@@ -2,7 +2,8 @@
 # in its own container, pulled from a registry.
 #
 #   cd Docker
-#   WARP_SERVER_NAME=matrix.example.org docker compose -f docker-compose.sqlite.prod.yml up -d
+#   cp .env.example .env      # then edit it
+#   docker compose -f docker-compose.sqlite.prod.yml up -d
 #
 # Homeserver http://localhost:8008, admin panel http://localhost:8009, web
 # client http://localhost:8080. The database, signing key and media live
@@ -30,12 +31,9 @@ services:
     entrypoint: ["/bin/sh", "-c"]
     command:
       - test -f /data/signing.key || warp generate-keys --output /data/signing.key; exec warp serve
+    env_file: .env
     environment:
-      WARP_SERVER_NAME: ${WARP_SERVER_NAME:-localhost}
-      WARP_WELL_KNOWN_CLIENT_BASE_URL: ${WARP_PUBLIC_BASEURL:-http://localhost:8008}
       WARP_DB_DRIVER: sqlite
-      WARP_REGISTRATION_ENABLED: ${WARP_REGISTRATION_ENABLED:-false}
-      WARP_FEDERATION_ENABLED: ${WARP_FEDERATION_ENABLED:-false}
     volumes:
       - warp-data:/data
     ports:
@@ -47,6 +45,7 @@ services:
     restart: unless-stopped
     depends_on:
       - warp
+    env_file: .env
     environment:
       WARP_ADMIN_HOMESERVER: http://warp:8008
     ports:
@@ -58,6 +57,7 @@ services:
     restart: unless-stopped
     depends_on:
       - warp
+    env_file: .env
     environment:
       WARP_WEB_HOMESERVER: http://warp:8008
     ports: