feat(cli): add login command and refactor shared helpers

internal/agent/disk.go

@@ -0,0 +1,25 @@
+package agent
+
+import (
+	"io/fs"
+	"path/filepath"
+)
+
+// DirSize returns the total size in bytes of all files under dir.
+func DirSize(dir string) (int64, error) {
+	var size int64
+	err := filepath.WalkDir(dir, func(_ string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return nil // skip unreadable entries
+		}
+		if !d.IsDir() {
+			info, err := d.Info()
+			if err != nil {
+				return nil
+			}
+			size += info.Size()
+		}
+		return nil
+	})
+	return size, err
+}