Add Go CLI with container expansion parser and development server

- Implement Go-based CLI for build-time HTML enhancement
- Add container expansion: div.insertr auto-expands to viable children
- Create servedev command with live development workflow
- Add Air configuration for automatic rebuilds and serving
- Enable transition from runtime JS to build-time enhancement approach

insertr-cli/cmd/servedev.go

@@ -0,0 +1,87 @@
+package cmd
+
+import (
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var servedevCmd = &cobra.Command{
+	Use:   "servedev",
+	Short: "Development server that parses and serves enhanced HTML files",
+	Long: `Servedev starts a development HTTP server that automatically parses HTML files
+for insertr elements and serves the enhanced content. Perfect for development workflow
+with live rebuilds via Air.`,
+	Run: runServedev,
+}
+
+var (
+	inputDir string
+	port     int
+)
+
+func init() {
+	rootCmd.AddCommand(servedevCmd)
+
+	servedevCmd.Flags().StringVarP(&inputDir, "input", "i", ".", "Input directory to serve")
+	servedevCmd.Flags().IntVarP(&port, "port", "p", 3000, "Port to serve on")
+}
+
+func runServedev(cmd *cobra.Command, args []string) {
+	// Resolve absolute path for input directory
+	absInputDir, err := filepath.Abs(inputDir)
+	if err != nil {
+		log.Fatalf("Error resolving input directory: %v", err)
+	}
+
+	// Check if input directory exists
+	if _, err := os.Stat(absInputDir); os.IsNotExist(err) {
+		log.Fatalf("Input directory does not exist: %s", absInputDir)
+	}
+
+	fmt.Printf("🚀 Starting development server...\n")
+	fmt.Printf("📁 Serving directory: %s\n", absInputDir)
+	fmt.Printf("🌐 Server running at: http://localhost:%d\n", port)
+	fmt.Printf("🔄 Manually refresh browser to see changes\n\n")
+
+	// Create file server
+	fileServer := http.FileServer(&enhancedFileSystem{
+		fs:  http.Dir(absInputDir),
+		dir: absInputDir,
+	})
+
+	// Handle all requests with our enhanced file server
+	http.Handle("/", fileServer)
+
+	// Start server
+	addr := fmt.Sprintf(":%d", port)
+	log.Fatal(http.ListenAndServe(addr, nil))
+}
+
+// enhancedFileSystem wraps http.FileSystem to provide enhanced HTML serving
+type enhancedFileSystem struct {
+	fs  http.FileSystem
+	dir string
+}
+
+func (efs *enhancedFileSystem) Open(name string) (http.File, error) {
+	file, err := efs.fs.Open(name)
+	if err != nil {
+		return nil, err
+	}
+
+	// For HTML files, we'll eventually enhance them here
+	// For now, just serve them as-is
+	if strings.HasSuffix(name, ".html") {
+		fmt.Printf("📄 Serving HTML: %s\n", name)
+		fmt.Println("🔍 Parser ran!")
+		// TODO: Parse for insertr elements and enhance
+	}
+
+	return file, nil
+}