Add bd reopen command for explicit issue reopening

Implements bd-235: New reopen command makes reopening issues more explicit
than 'bd update --status open'.

Features:
- Sets status to 'open' and automatically clears closed_at
- Emits EventReopened via UpdateIssue
- Optional --reason flag to add comment
- JSON output support
- Auto-flush after operation

Closes: bd-234, bd-235, bd-236, bd-237, bd-238, bd-239
Related: bd-224 (status/closed_at invariant enforcement)
Amp-Thread-ID: https://ampcode.com/threads/T-b1c82629-3521-440f-9f16-ab6d66fb5091
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/reopen.go

@@ -0,0 +1,71 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"os"
+
+	"github.com/fatih/color"
+	"github.com/spf13/cobra"
+	"github.com/steveyegge/beads/internal/types"
+)
+
+var reopenCmd = &cobra.Command{
+	Use:   "reopen [id...]",
+	Short: "Reopen one or more closed issues",
+	Long: `Reopen closed issues by setting status to 'open' and clearing the closed_at timestamp.
+
+This is more explicit than 'bd update --status open' and emits a Reopened event.`,
+	Args: cobra.MinimumNArgs(1),
+	Run: func(cmd *cobra.Command, args []string) {
+		reason, _ := cmd.Flags().GetString("reason")
+
+		ctx := context.Background()
+		reopenedIssues := []*types.Issue{}
+		for _, id := range args {
+			// UpdateIssue automatically clears closed_at when status changes from closed
+			updates := map[string]interface{}{
+				"status": string(types.StatusOpen),
+			}
+			if err := store.UpdateIssue(ctx, id, updates, actor); err != nil {
+				fmt.Fprintf(os.Stderr, "Error reopening %s: %v\n", id, err)
+				continue
+			}
+
+			// Add reason as a comment if provided
+			if reason != "" {
+				if err := store.AddComment(ctx, id, actor, reason); err != nil {
+					fmt.Fprintf(os.Stderr, "Warning: failed to add comment to %s: %v\n", id, err)
+				}
+			}
+
+			if jsonOutput {
+				issue, _ := store.GetIssue(ctx, id)
+				if issue != nil {
+					reopenedIssues = append(reopenedIssues, issue)
+				}
+			} else {
+				blue := color.New(color.FgBlue).SprintFunc()
+				reasonMsg := ""
+				if reason != "" {
+					reasonMsg = ": " + reason
+				}
+				fmt.Printf("%s Reopened %s%s\n", blue("↻"), id, reasonMsg)
+			}
+		}
+
+		// Schedule auto-flush if any issues were reopened
+		if len(args) > 0 {
+			markDirtyAndScheduleFlush()
+		}
+
+		if jsonOutput && len(reopenedIssues) > 0 {
+			outputJSON(reopenedIssues)
+		}
+	},
+}
+
+func init() {
+	reopenCmd.Flags().StringP("reason", "r", "", "Reason for reopening")
+	rootCmd.AddCommand(reopenCmd)
+}