Fix N+1 query pattern in export operations (bd-rcmg)

**Problem**: Export operations called GetLabels() and GetIssueComments()
in a loop for each issue, creating N+1 query pattern. For 100 issues
this created 201 queries instead of 3-5.

**Solution**:
- Added GetCommentsForIssues() batch method to storage interface
- Implemented batch method in SQLite and memory storage backends
- Updated handleExport() and triggerExport() to use batch queries
- Added comprehensive tests for batch operations

**Impact**: Query count reduced from ~201 to ~3-5 for 100 issues.

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

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

internal/storage/sqlite/batch_test.go

@@ -0,0 +1,143 @@
+package sqlite
+
+import (
+	"context"
+	"testing"
+
+	"github.com/steveyegge/beads/internal/types"
+)
+
+// TestBatchGetLabelsAndComments verifies that GetLabelsForIssues and GetCommentsForIssues
+// correctly fetch data for multiple issues in a single query (avoiding N+1 pattern)
+func TestBatchGetLabelsAndComments(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Create test issues
+	issues := []*types.Issue{
+		{
+			ID:        "bd-batch1",
+			Title:     "Issue 1",
+			IssueType: types.TypeTask,
+			Status:    types.StatusOpen,
+			Priority:  1,
+		},
+		{
+			ID:        "bd-batch2",
+			Title:     "Issue 2",
+			IssueType: types.TypeTask,
+			Status:    types.StatusOpen,
+			Priority:  1,
+		},
+		{
+			ID:        "bd-batch3",
+			Title:     "Issue 3",
+			IssueType: types.TypeTask,
+			Status:    types.StatusOpen,
+			Priority:  1,
+		},
+	}
+
+	for _, issue := range issues {
+		if err := store.CreateIssue(ctx, issue, "test-actor"); err != nil {
+			t.Fatalf("Failed to create issue %s: %v", issue.ID, err)
+		}
+	}
+
+	// Add labels to issues
+	if err := store.AddLabel(ctx, "bd-batch1", "bug", "test-actor"); err != nil {
+		t.Fatalf("Failed to add label: %v", err)
+	}
+	if err := store.AddLabel(ctx, "bd-batch1", "urgent", "test-actor"); err != nil {
+		t.Fatalf("Failed to add label: %v", err)
+	}
+	if err := store.AddLabel(ctx, "bd-batch2", "feature", "test-actor"); err != nil {
+		t.Fatalf("Failed to add label: %v", err)
+	}
+	// bd-batch3 has no labels
+
+	// Add comments to issues
+	if _, err := store.AddIssueComment(ctx, "bd-batch1", "alice", "First comment"); err != nil {
+		t.Fatalf("Failed to add comment: %v", err)
+	}
+	if _, err := store.AddIssueComment(ctx, "bd-batch1", "bob", "Second comment"); err != nil {
+		t.Fatalf("Failed to add comment: %v", err)
+	}
+	if _, err := store.AddIssueComment(ctx, "bd-batch3", "charlie", "Comment on bd-batch3"); err != nil {
+		t.Fatalf("Failed to add comment: %v", err)
+	}
+	// bd-batch2 has no comments
+
+	// Test batch get labels
+	issueIDs := []string{"bd-batch1", "bd-batch2", "bd-batch3"}
+	allLabels, err := store.GetLabelsForIssues(ctx, issueIDs)
+	if err != nil {
+		t.Fatalf("GetLabelsForIssues failed: %v", err)
+	}
+
+	// Verify labels
+	if len(allLabels["bd-batch1"]) != 2 {
+		t.Errorf("Expected 2 labels for bd-batch1, got %d", len(allLabels["bd-batch1"]))
+	}
+	if len(allLabels["bd-batch2"]) != 1 {
+		t.Errorf("Expected 1 label for bd-batch2, got %d", len(allLabels["bd-batch2"]))
+	}
+	if len(allLabels["bd-batch3"]) != 0 {
+		t.Errorf("Expected 0 labels for bd-batch3, got %d", len(allLabels["bd-batch3"]))
+	}
+
+	// Test batch get comments
+	allComments, err := store.GetCommentsForIssues(ctx, issueIDs)
+	if err != nil {
+		t.Fatalf("GetCommentsForIssues failed: %v", err)
+	}
+
+	// Verify comments
+	if len(allComments["bd-batch1"]) != 2 {
+		t.Errorf("Expected 2 comments for bd-batch1, got %d", len(allComments["bd-batch1"]))
+	}
+	if allComments["bd-batch1"][0].Author != "alice" {
+		t.Errorf("Expected first comment author to be 'alice', got %s", allComments["bd-batch1"][0].Author)
+	}
+	if allComments["bd-batch1"][1].Author != "bob" {
+		t.Errorf("Expected second comment author to be 'bob', got %s", allComments["bd-batch1"][1].Author)
+	}
+
+	if len(allComments["bd-batch2"]) != 0 {
+		t.Errorf("Expected 0 comments for bd-batch2, got %d", len(allComments["bd-batch2"]))
+	}
+
+	if len(allComments["bd-batch3"]) != 1 {
+		t.Errorf("Expected 1 comment for bd-batch3, got %d", len(allComments["bd-batch3"]))
+	}
+	if len(allComments["bd-batch3"]) > 0 && allComments["bd-batch3"][0].Author != "charlie" {
+		t.Errorf("Expected comment author to be 'charlie', got %s", allComments["bd-batch3"][0].Author)
+	}
+}
+
+// TestBatchGetEmptyIssueIDs verifies that batch methods handle empty issue ID lists
+func TestBatchGetEmptyIssueIDs(t *testing.T) {
+	store, cleanup := setupTestDB(t)
+	defer cleanup()
+
+	ctx := context.Background()
+
+	// Test with empty issue ID list
+	labels, err := store.GetLabelsForIssues(ctx, []string{})
+	if err != nil {
+		t.Fatalf("GetLabelsForIssues with empty list failed: %v", err)
+	}
+	if len(labels) != 0 {
+		t.Errorf("Expected empty map, got %d entries", len(labels))
+	}
+
+	comments, err := store.GetCommentsForIssues(ctx, []string{})
+	if err != nil {
+		t.Fatalf("GetCommentsForIssues with empty list failed: %v", err)
+	}
+	if len(comments) != 0 {
+		t.Errorf("Expected empty map, got %d entries", len(comments))
+	}
+}