feat(destroy): implement destroy command parity

internal/homesick/core/core.go

@@ -165,6 +165,33 @@ func (a *App) Commit(castle string, message string) error {
 	return runGitWithIO(castledir, a.Stdout, a.Stderr, "commit", "-m", trimmedMessage)
 }
 
+func (a *App) Destroy(castle string) error {
+	if strings.TrimSpace(castle) == "" {
+		castle = "dotfiles"
+	}
+
+	castleRoot := filepath.Join(a.ReposDir, castle)
+	castleInfo, err := os.Lstat(castleRoot)
+	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return fmt.Errorf("castle %q not found", castle)
+		}
+		return err
+	}
+
+	// Only attempt unlinking managed home files for regular castle directories.
+	if castleInfo.Mode()&os.ModeSymlink == 0 {
+		castleHome := filepath.Join(castleRoot, "home")
+		if info, statErr := os.Stat(castleHome); statErr == nil && info.IsDir() {
+			if unlinkErr := a.UnlinkCastle(castle); unlinkErr != nil {
+				return unlinkErr
+			}
+		}
+	}
+
+	return os.RemoveAll(castleRoot)
+}
+
 func (a *App) Link(castle string) error {
 	if strings.TrimSpace(castle) == "" {
 		castle = "dotfiles"