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>

README.md

@@ -25,9 +25,9 @@ CLI, `bash` and `gzip`.
 On the **source** host:
 
 ```bash
-git clone <this repo> docker-migrate && cd docker-migrate
+git clone <this repo> dockmv && cd dockmv
 docker compose up -d --build
-docker compose logs docker-migrate      # prints the URL, including the access token
+docker compose logs dockmv      # prints the URL, including the access token
 ```
 
 Then open the printed URL. It binds to `127.0.0.1` only; reach it from your laptop with a tunnel:
@@ -42,16 +42,16 @@ The binary is fully static and embeds the web UI, so there is nothing to install
 
 ```bash
 make build          # needs Go 1.25+ and Node 20+ ... or just `go build .` if you skip the UI rebuild
-./docker-migrate serve
+./dockmv serve
 ```
 
 Prebuilt for several platforms:
 
 ```bash
-make release        # dist/docker-migrate-linux-amd64, -linux-arm64, -darwin-arm64, -windows-amd64
+make release        # dist/dockmv-linux-amd64, -linux-arm64, -darwin-arm64, -windows-amd64
 ```
 
-`docker-migrate` needs access to the Docker socket on the source host, so run it as a user in the
+`dockmv` needs access to the Docker socket on the source host, so run it as a user in the
 `docker` group (or as root).
 
 ---
@@ -206,9 +206,9 @@ free disk space and architecture.
 ## Command line
 
 ```
-docker-migrate [serve] [flags]     start the web interface (default)
-docker-migrate inspect [flags]     print the source inventory as JSON
-docker-migrate version
+dockmv [serve] [flags]     start the web interface (default)
+dockmv inspect [flags]     print the source inventory as JSON
+dockmv version
 ```
 
 `serve` flags:
@@ -225,7 +225,7 @@ docker-migrate version
 `inspect` is handy for scripting and for reporting bugs:
 
 ```bash
-docker-migrate inspect --sizes | jq '.containers[] | {name, image, mounts}'
+dockmv inspect --sizes | jq '.containers[] | {name, image, mounts}'
 ```
 
 ---