Optimize bd list: replace N+1 label queries with bulk fetch

Problem:
In direct mode, bd list was making a separate GetLabels() call for
each issue when displaying labels. With 538 issues, this resulted in
538 separate database queries.

While investigating the reported 5+ second slowness, discovered this
N+1 query issue that would impact performance with many issues.

Solution:
1. Added GetLabelsForIssues(issueIDs []string) to Storage interface
2. Implemented bulk fetch in SQLite (already existed, now exposed)
3. Implemented bulk fetch in MemoryStorage
4. Updated list.go to fetch all labels in single query

Changes:
- internal/storage/storage.go: Add GetLabelsForIssues to interface
- internal/storage/memory/memory.go: Implement GetLabelsForIssues
- cmd/bd/list.go: Use bulk fetching in all output modes

Impact:
Eliminates N queries for labels, replacing with 1 bulk query.
This optimization applies to direct mode only (daemon mode already
uses bulk operations via RPC).

Note: The reported 5s slowness was actually caused by daemon auto-start
timeout. Use --no-daemon flag or run 'bd migrate --update-repo-id' to
resolve the legacy database issue causing daemon startup failures.

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

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

internal/storage/memory/memory.go

@@ -791,6 +791,19 @@ func (m *MemoryStorage) GetLabels(ctx context.Context, issueID string) ([]string
 	return m.labels[issueID], nil
 }
 
+func (m *MemoryStorage) GetLabelsForIssues(ctx context.Context, issueIDs []string) (map[string][]string, error) {
+	m.mu.RLock()
+	defer m.mu.RUnlock()
+
+	result := make(map[string][]string)
+	for _, issueID := range issueIDs {
+		if labels, exists := m.labels[issueID]; exists {
+			result[issueID] = labels
+		}
+	}
+	return result, nil
+}
+
 func (m *MemoryStorage) GetIssuesByLabel(ctx context.Context, label string) ([]*types.Issue, error) {
 	m.mu.RLock()
 	defer m.mu.RUnlock()

internal/storage/storage.go

@@ -35,6 +35,7 @@ type Storage interface {
 	AddLabel(ctx context.Context, issueID, label, actor string) error
 	RemoveLabel(ctx context.Context, issueID, label, actor string) error
 	GetLabels(ctx context.Context, issueID string) ([]string, error)
+	GetLabelsForIssues(ctx context.Context, issueIDs []string) (map[string][]string, error)
 	GetIssuesByLabel(ctx context.Context, label string) ([]*types.Issue, error)
 
 	// Ready Work & Blocking