fix: support delete in --no-db mode (GH#822)

Add CreateTombstone() to MemoryStorage and deleteBatchFallback() to
handle deletion when SQLite is not available. This fixes the error
"tombstone operation not supported by this storage backend" when
using bd delete with --no-db flag.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/storage/memory/memory.go

@@ -474,6 +474,41 @@ func (m *MemoryStorage) CloseIssue(ctx context.Context, id string, reason string
 	}, actor)
 }
 
+// CreateTombstone converts an existing issue to a tombstone record.
+// This is a soft-delete that preserves the issue with status="tombstone".
+func (m *MemoryStorage) CreateTombstone(ctx context.Context, id string, actor string, reason string) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	issue, ok := m.issues[id]
+	if !ok {
+		return fmt.Errorf("issue not found: %s", id)
+	}
+
+	now := time.Now()
+	issue.OriginalType = string(issue.IssueType)
+	issue.Status = types.StatusTombstone
+	issue.DeletedAt = &now
+	issue.DeletedBy = actor
+	issue.DeleteReason = reason
+	issue.UpdatedAt = now
+
+	// Mark as dirty for export
+	m.dirty[id] = true
+
+	// Record tombstone creation event
+	event := &types.Event{
+		IssueID:   id,
+		EventType: "deleted",
+		Actor:     actor,
+		Comment:   &reason,
+		CreatedAt: now,
+	}
+	m.events[id] = append(m.events[id], event)
+
+	return nil
+}
+
 // DeleteIssue permanently deletes an issue and all associated data
 func (m *MemoryStorage) DeleteIssue(ctx context.Context, id string) error {
 	m.mu.Lock()

internal/storage/memory/memory_test.go

@@ -2,6 +2,7 @@ package memory
 
 import (
 	"context"
+	"strings"
 	"testing"
 	"time"
 
@@ -949,6 +950,68 @@ func TestStatistics_TombstonesExcludedFromTotal(t *testing.T) {
 	}
 }
 
+func TestCreateTombstone(t *testing.T) {
+	store := setupTestMemory(t)
+	defer store.Close()
+
+	ctx := context.Background()
+
+	// Create an issue
+	issue := &types.Issue{
+		Title:     "Test Issue",
+		Status:    types.StatusOpen,
+		Priority:  1,
+		IssueType: types.TypeTask,
+	}
+	if err := store.CreateIssue(ctx, issue, "test"); err != nil {
+		t.Fatalf("CreateIssue failed: %v", err)
+	}
+	issueID := issue.ID
+
+	// Create tombstone
+	if err := store.CreateTombstone(ctx, issueID, "test-actor", "test deletion"); err != nil {
+		t.Fatalf("CreateTombstone failed: %v", err)
+	}
+
+	// Verify the issue is now a tombstone
+	updated, err := store.GetIssue(ctx, issueID)
+	if err != nil {
+		t.Fatalf("GetIssue failed: %v", err)
+	}
+
+	if updated.Status != types.StatusTombstone {
+		t.Errorf("Expected status=%s, got %s", types.StatusTombstone, updated.Status)
+	}
+	if updated.DeletedAt == nil {
+		t.Error("Expected DeletedAt to be set")
+	}
+	if updated.DeletedBy != "test-actor" {
+		t.Errorf("Expected DeletedBy=test-actor, got %s", updated.DeletedBy)
+	}
+	if updated.DeleteReason != "test deletion" {
+		t.Errorf("Expected DeleteReason='test deletion', got %s", updated.DeleteReason)
+	}
+	if updated.OriginalType != string(types.TypeTask) {
+		t.Errorf("Expected OriginalType=%s, got %s", types.TypeTask, updated.OriginalType)
+	}
+}
+
+func TestCreateTombstone_NotFound(t *testing.T) {
+	store := setupTestMemory(t)
+	defer store.Close()
+
+	ctx := context.Background()
+
+	// Try to create tombstone for non-existent issue
+	err := store.CreateTombstone(ctx, "nonexistent", "test", "reason")
+	if err == nil {
+		t.Fatal("Expected error for non-existent issue")
+	}
+	if !strings.Contains(err.Error(), "not found") {
+		t.Errorf("Expected 'not found' error, got: %v", err)
+	}
+}
+
 func TestConfigOperations(t *testing.T) {
 	store := setupTestMemory(t)
 	defer store.Close()