feat(cli): implement exec and exec_all commands

internal/homesick/core/core.go

@@ -219,6 +219,75 @@ func (a *App) Open(castle string) error {
 	return nil
 }
 
+func (a *App) Exec(castle string, command []string) error {
+	commandString := strings.TrimSpace(strings.Join(command, " "))
+	if commandString == "" {
+		return errors.New("exec requires COMMAND")
+	}
+
+	castleRoot := filepath.Join(a.ReposDir, castle)
+	if _, err := os.Stat(castleRoot); err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return fmt.Errorf("castle %q not found", castle)
+		}
+		return err
+	}
+
+	cmd := exec.Command("sh", "-c", commandString)
+	cmd.Dir = castleRoot
+	cmd.Stdout = a.Stdout
+	cmd.Stderr = a.Stderr
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("exec failed: %w", err)
+	}
+
+	return nil
+}
+
+func (a *App) ExecAll(command []string) error {
+	commandString := strings.TrimSpace(strings.Join(command, " "))
+	if commandString == "" {
+		return errors.New("exec_all requires COMMAND")
+	}
+
+	if _, err := os.Stat(a.ReposDir); err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return nil
+		}
+		return err
+	}
+
+	var castles []string
+	err := filepath.WalkDir(a.ReposDir, func(path string, d fs.DirEntry, walkErr error) error {
+		if walkErr != nil {
+			return walkErr
+		}
+		if !d.IsDir() || d.Name() != ".git" {
+			return nil
+		}
+
+		castleRoot := filepath.Dir(path)
+		rel, err := filepath.Rel(a.ReposDir, castleRoot)
+		if err != nil {
+			return err
+		}
+		castles = append(castles, rel)
+		return filepath.SkipDir
+	})
+	if err != nil {
+		return err
+	}
+
+	sort.Strings(castles)
+	for _, castle := range castles {
+		if err := a.Exec(castle, []string{commandString}); err != nil {
+			return fmt.Errorf("exec_all failed for %q: %w", castle, err)
+		}
+	}
+
+	return nil
+}
+
 func (a *App) Generate(castlePath string) error {
 	trimmed := strings.TrimSpace(castlePath)
 	if trimmed == "" {