Fix module path and restore cmd/ omitted by gitignore

Rename module github.com/johnellis/stalwart-migrator ->
github.com/LINUXexpert-org/stalwart-migrator to match the repository
location, so the module resolves under `go get`.

The initial commit's .gitignore listed the compiled binary as a bare
`stalwart-migrate` pattern, which Git matches at any depth -- so it also
excluded the cmd/stalwart-migrate/ source directory, and the initial
commit shipped without the CLI entrypoint. Anchor the pattern to the
repo root as /stalwart-migrate and add the four missing files.

go build, go vet, and go test ./... all pass.

cmd/stalwart-migrate/status.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+
+	"github.com/LINUXexpert-org/stalwart-migrator/internal/checkpoint"
+)
+
+func runStatus(args []string) error {
+	fs := flag.NewFlagSet("status", flag.ExitOnError)
+	stateDir := fs.String("state-dir", checkpoint.DefaultBaseDir, "directory runs are checkpointed in")
+	if err := fs.Parse(args); err != nil {
+		return err
+	}
+
+	store := checkpoint.NewStore(*stateDir)
+
+	if fs.NArg() == 0 {
+		ids, err := store.List()
+		if err != nil {
+			return fmt.Errorf("list runs: %w", err)
+		}
+		if len(ids) == 0 {
+			fmt.Println("no runs found in", *stateDir)
+			return nil
+		}
+		fmt.Println("runs (newest first):")
+		for _, id := range ids {
+			fmt.Println(" ", id)
+		}
+		return nil
+	}
+
+	runID := fs.Arg(0)
+	rs, err := store.Load(runID)
+	if err != nil {
+		return fmt.Errorf("load run %s: %w", runID, err)
+	}
+
+	fmt.Printf("run:    %s\n", rs.RunID)
+	fmt.Printf("source: %s\n", rs.SourceVersion)
+	fmt.Printf("target: %s\n", rs.TargetVersion)
+	fmt.Printf("topology: deployment=%s store=%s\n", rs.Topology.DeploymentKind, rs.Topology.StoreBackend)
+	fmt.Printf("rollback window closed: %v\n", rs.RollbackWindowClosed)
+	fmt.Println("steps:")
+	for _, step := range rs.Steps {
+		tag := string(step.Status)
+		if step.Verdict != "" {
+			tag = step.Verdict
+		}
+		line := fmt.Sprintf("  [%-4s] %s/%s", tag, step.Phase, step.Name)
+		if step.Detail != "" {
+			line += " - " + step.Detail
+		}
+		if step.Error != "" {
+			line += " (error: " + step.Error + ")"
+		}
+		fmt.Println(line)
+	}
+	return nil
+}