Add file exclusion support (sgard exclude/include).

Paths added to the manifest's exclude list are skipped during Add,
MirrorUp, and MirrorDown directory walks. Excluding a directory
excludes everything under it. Already-tracked entries matching a
new exclusion are removed from the manifest.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cmd/sgard/exclude.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"fmt"
+
+	"github.com/kisom/sgard/garden"
+	"github.com/spf13/cobra"
+)
+
+var listExclude bool
+
+var excludeCmd = &cobra.Command{
+	Use:   "exclude [path...]",
+	Short: "Exclude paths from tracking",
+	Long:  "Add paths to the exclusion list. Excluded paths are skipped during add and mirror operations. Use --list to show current exclusions.",
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		if listExclude {
+			for _, p := range g.GetManifest().Exclude {
+				fmt.Println(p)
+			}
+			return nil
+		}
+
+		if len(args) == 0 {
+			return fmt.Errorf("provide paths to exclude, or use --list")
+		}
+
+		if err := g.Exclude(args); err != nil {
+			return err
+		}
+
+		fmt.Printf("Excluded %d path(s)\n", len(args))
+		return nil
+	},
+}
+
+var includeCmd = &cobra.Command{
+	Use:   "include <path>...",
+	Short: "Remove paths from the exclusion list",
+	Args:  cobra.MinimumNArgs(1),
+	RunE: func(cmd *cobra.Command, args []string) error {
+		g, err := garden.Open(repoFlag)
+		if err != nil {
+			return err
+		}
+
+		if err := g.Include(args); err != nil {
+			return err
+		}
+
+		fmt.Printf("Included %d path(s)\n", len(args))
+		return nil
+	},
+}
+
+func init() {
+	excludeCmd.Flags().BoolVarP(&listExclude, "list", "l", false, "list current exclusions")
+	rootCmd.AddCommand(excludeCmd)
+	rootCmd.AddCommand(includeCmd)
+}