feat(cli): add promote, cards, copy, demote, delete, edit commands

Complete CLI crystallization loop. Promote generates card_data
(template slots, checklist steps, link URLs). Cards view sorted by
use_count. Copy increments usage. Demote strips card layer. Delete
does soft then hard. Edit opens $EDITOR.

cmd/cards.go

@@ -0,0 +1,73 @@
+package cmd
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/lerko/nib/internal/db"
+	"github.com/lerko/nib/internal/display"
+	"github.com/spf13/cobra"
+)
+
+var (
+	cardsTag  string
+	cardsType string
+)
+
+var cardsCmd = &cobra.Command{
+	Use:   "cards",
+	Short: "list crystallized cards by usage",
+	RunE:  runCards,
+}
+
+func init() {
+	cardsCmd.Flags().StringVar(&cardsTag, "tag", "", "filter by tag")
+	cardsCmd.Flags().StringVar(&cardsType, "type", "", "filter by card type")
+	rootCmd.AddCommand(cardsCmd)
+}
+
+func runCards(_ *cobra.Command, _ []string) error {
+	store, err := openStore()
+	if err != nil {
+		return err
+	}
+	defer store.Close()
+
+	p := db.DefaultListParams()
+	p.CardsOnly = true
+	p.Sort = "use_count"
+	p.Order = "desc"
+
+	if cardsTag != "" {
+		p.Tag = &cardsTag
+	}
+	if cardsType != "" {
+		if !db.ValidCardType(cardsType) {
+			return fmt.Errorf("invalid_type — %q is not a valid card type", cardsType)
+		}
+		ct := db.CardType(cardsType)
+		p.CardTypeFilter = &ct
+	}
+
+	entities, err := store.List(p)
+	if err != nil {
+		return err
+	}
+
+	for _, e := range entities {
+		glyph := display.DisplayGlyph(e.Glyph, e.CardType)
+		shortID := display.FormatID(e.ID)
+
+		var tagStr string
+		for _, tag := range e.Tags {
+			tagStr += " #" + tag
+		}
+
+		fmt.Printf("%s  %-40s %-16s %3d×  %s\n",
+			glyph, e.Body,
+			strings.TrimSpace(tagStr),
+			e.UseCount, shortID)
+	}
+
+	return nil
+}