feat(tombstone): add P2 code review improvements (bd-saa, bd-1bu, bd-nyt)

- Add partial index on deleted_at for efficient TTL queries
- Exclude tombstones from SearchIssues by default (new IncludeTombstones filter)
- Report tombstone count separately in GetStatistics
- Display tombstone count in bd stats output

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

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

internal/storage/sqlite/events.go

@@ -110,15 +110,16 @@ func (s *SQLiteStorage) GetEvents(ctx context.Context, issueID string, limit int
 func (s *SQLiteStorage) GetStatistics(ctx context.Context) (*types.Statistics, error) {
 	var stats types.Statistics
 
-	// Get counts
+	// Get counts (bd-nyt: exclude tombstones from TotalIssues, report separately)
 	err := s.db.QueryRowContext(ctx, `
 		SELECT
-			COUNT(*) as total,
+			COALESCE(SUM(CASE WHEN status != 'tombstone' THEN 1 ELSE 0 END), 0) as total,
 			COALESCE(SUM(CASE WHEN status = 'open' THEN 1 ELSE 0 END), 0) as open,
 			COALESCE(SUM(CASE WHEN status = 'in_progress' THEN 1 ELSE 0 END), 0) as in_progress,
-			COALESCE(SUM(CASE WHEN status = 'closed' THEN 1 ELSE 0 END), 0) as closed
+			COALESCE(SUM(CASE WHEN status = 'closed' THEN 1 ELSE 0 END), 0) as closed,
+			COALESCE(SUM(CASE WHEN status = 'tombstone' THEN 1 ELSE 0 END), 0) as tombstone
 		FROM issues
-	`).Scan(&stats.TotalIssues, &stats.OpenIssues, &stats.InProgressIssues, &stats.ClosedIssues)
+	`).Scan(&stats.TotalIssues, &stats.OpenIssues, &stats.InProgressIssues, &stats.ClosedIssues, &stats.TombstoneIssues)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get issue counts: %w", err)
 	}