Rename product to dockmv (container, image, module, env vars)

Container/image/service name, Go module path, CLI binary name, and
DOCKER_MIGRATE_* env vars still used the old working name; the project
is branded DockMV everywhere else (README, logo, Gitea repo).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docker-compose.yml

@@ -1,20 +1,20 @@
-# docker-migrate, running on the SOURCE host.
+# dockmv, running on the SOURCE host.
 #
 #   docker compose up -d
-#   docker compose logs docker-migrate   # the URL and access token are printed here
+#   docker compose logs dockmv   # the URL and access token are printed here
 #
 # The container needs the Docker socket to read containers and stream their
 # data. That is equivalent to root on this host, so the UI is protected by a
 # generated token and should not be published to an untrusted network.
 
 services:
-  docker-migrate:
+  dockmv:
     build:
       context: .
       args:
         VERSION: ${VERSION:-dev}
-    image: docker-migrate:latest
-    container_name: docker-migrate
+    image: dockmv:latest
+    container_name: dockmv
     restart: unless-stopped
     ports:
       # Bind to loopback only. Use an SSH tunnel to reach it from elsewhere:
@@ -26,7 +26,7 @@ services:
       - migrate-data:/data
     environment:
       # Set a fixed token to keep the same URL across restarts.
-      # DOCKER_MIGRATE_TOKEN: change-me
+      # DOCKMV_TOKEN: change-me
       TZ: ${TZ:-UTC}
     command:
       - serve