feat(cli): add nib add + nib ls commands

Default command delegation: `nib "..."` routes to `nib add`. Capture
bar parses grammar, creates entities. `nib ls` lists with date
grouping, tag filter, 48h default window. Display glyphs for all
entity types.

cmd/root.go

@@ -0,0 +1,52 @@
+package cmd
+
+import (
+	"os"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+var rootCmd = &cobra.Command{
+	Use:   "nib",
+	Short: "capture and crystallize notes, todos, and events",
+	Args:  cobra.ArbitraryArgs,
+	RunE: func(cmd *cobra.Command, args []string) error {
+		if len(args) == 0 {
+			return cmd.Help()
+		}
+		return runAdd(cmd, args)
+	},
+	SilenceUsage: true,
+}
+
+func Execute() error {
+	if len(os.Args) > 1 {
+		first := os.Args[1]
+		isFlag := strings.HasPrefix(first, "-") && !strings.Contains(first, " ")
+		if first != "help" && first != "completion" &&
+			!isFlag && !isSubcommand(first) {
+			rootCmd.SetArgs(append([]string{"add", "--"}, os.Args[1:]...))
+		}
+	}
+	return rootCmd.Execute()
+}
+
+func isSubcommand(name string) bool {
+	for _, c := range rootCmd.Commands() {
+		if c.Name() == name {
+			return true
+		}
+		for _, alias := range c.Aliases {
+			if alias == name {
+				return true
+			}
+		}
+	}
+	return false
+}
+
+func init() {
+	rootCmd.AddCommand(addCmd)
+	rootCmd.AddCommand(lsCmd)
+}