add a stub for Caddyfile controller

internal/machine/caddyfile/controller.go

@@ -0,0 +1,35 @@
+package caddyfile
+
+import (
+	"context"
+	"fmt"
+	"os"
+	"path/filepath"
+	"sync"
+	"uncloud/internal/machine/store"
+)
+
+// Controller monitors container changes in the cluster store and generates a configuration file for Caddy reverse
+// proxy. The generated Caddyfile allows Caddy to route external traffic to service containers across the internal
+// network.
+type Controller struct {
+	store *store.Store
+	path  string
+	mu    sync.Mutex
+}
+
+func NewController(store *store.Store, path string) (*Controller, error) {
+	dir := filepath.Dir(path)
+	if err := os.MkdirAll(dir, 0755); err != nil {
+		return nil, fmt.Errorf("create parent directory for Caddyfile '%s': %w", dir, err)
+	}
+
+	return &Controller{
+		store: store,
+		path:  path,
+	}, nil
+}
+
+func (cc *Controller) Run(ctx context.Context) error {
+	return nil
+}