fix(import): preserve comment created_at timestamps during import (#735)

Comment timestamps were being overwritten with CURRENT_TIMESTAMP during
import, causing infinite sync loops between hosts as each import would
update timestamps.

Added ImportIssueComment() method that accepts and preserves the original
timestamp from JSONL, and updated importComments() to use it.

Closes #735

internal/importer/importer.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"sort"
 	"strings"
+	"time"
 
 	"github.com/steveyegge/beads/internal/config"
 	"github.com/steveyegge/beads/internal/linear"
@@ -892,7 +893,10 @@ func importComments(ctx context.Context, sqliteStore *sqlite.SQLiteStorage, issu
 		for _, comment := range issue.Comments {
 			key := fmt.Sprintf("%s:%s", comment.Author, strings.TrimSpace(comment.Text))
 			if !existingComments[key] {
-				if _, err := sqliteStore.AddIssueComment(ctx, issue.ID, comment.Author, comment.Text); err != nil {
+				// Use ImportIssueComment to preserve original timestamp (GH#735)
+				// Format timestamp as RFC3339 for SQLite compatibility
+				createdAt := comment.CreatedAt.UTC().Format(time.RFC3339)
+				if _, err := sqliteStore.ImportIssueComment(ctx, issue.ID, comment.Author, comment.Text, createdAt); err != nil {
 					if opts.Strict {
 						return fmt.Errorf("error adding comment to %s: %w", issue.ID, err)
 					}