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>

scripts/build-release.ps1

@@ -1,10 +1,10 @@
 #requires -Version 5.1
 <#
 .SYNOPSIS
-    Build the docker-migrate web UI and cross-compile release binaries.
+    Build the dockmv web UI and cross-compile release binaries.
 
 .DESCRIPTION
-    Produces dist/docker-migrate-<os>-<arch>[.exe] for every target, one archive
+    Produces dist/dockmv-<os>-<arch>[.exe] for every target, one archive
     per binary (.zip for Windows, .tar.gz elsewhere) and dist/SHA256SUMS.txt.
 
     The PowerShell equivalent of `make release`, so a Windows host without make
@@ -130,11 +130,11 @@ try {
         if (-not $Tag) { $Tag = "dev" }
     }
 
-    $bin     = "docker-migrate"
+    $bin     = "dockmv"
     $distDir = Join-Path $repoRoot "dist"
     $ldflags = "-s -w -X main.version=$Tag"
 
-    Write-Host "docker-migrate release build" -ForegroundColor Cyan
+    Write-Host "dockmv release build" -ForegroundColor Cyan
     Write-Host "  go      : $Go"
     Write-Host "  tag     : $Tag"
     Write-Host "  targets : $($Targets -join ', ')"
@@ -152,13 +152,17 @@ try {
     # run before the compile — not after, and not in parallel with it.
     if (-not $SkipUi) {
         Write-Host "Building web UI..." -ForegroundColor Cyan
-        if (-not (Get-Command npm -ErrorAction SilentlyContinue)) {
+        # npm.cmd, not npm(.ps1): the ps1 shim reparses $MyInvocation.Line as text
+        # when called via `& $Exe @Args`, which mangles splatted args into a bogus
+        # single token and makes npm print usage instead of running the command.
+        $npmCmd = (Get-Command npm.cmd -ErrorAction SilentlyContinue).Source
+        if (-not $npmCmd) {
             throw "npm not found — install Node 22+, or pass -SkipUi to reuse the committed internal/webui/dist."
         }
         Push-Location (Join-Path $repoRoot "web")
         try {
-            Invoke-Checked npm @("ci", "--no-audit", "--no-fund")
-            Invoke-Checked npm @("run", "build")
+            Invoke-Checked $npmCmd @("ci", "--no-audit", "--no-fund")
+            Invoke-Checked $npmCmd @("run", "build")
         }
         finally { Pop-Location }
         Write-Host ""