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>

internal/store/store.go

@@ -12,7 +12,7 @@ import (
 	"sort"
 	"sync"
 
-	"github.com/arescom/docker-migrate/internal/sshx"
+	"github.com/arescom/dockmv/internal/sshx"
 )
 
 // ErrNotFound is returned for an unknown connection id.