Add repository implementation for comment CRUD and thread queries. Handles PostgreSQL-specific operations including array marshaling for langs field and proper NULL handling for optional JSON fields. Key operations: - Create/Update/Delete with soft delete support - GetByURI with ErrCommentNotFound for missing records - ListByRoot/ListByParent for thread traversal - ListByCommenter for user history - CountByParent for pagination All queries filter out soft-deleted comments (deleted_at IS NULL). 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude <noreply@anthropic.com>