List Excel Templates

List user's saved Excel templates. Supports both authenticated users and guest mode.

Args: current_user: Authenticated user (optional for guest mode) limit: Maximum number of templates to return excel_type: Filter by type ('template' or 'filled')

Returns: { "templates": [ { "template_id": "uuid", "name": "filename.xlsx", "detected_fields": [...], "excel_type": "template" | "filled", "created_at": "2025-01-13T...", "last_used_at": "2025-01-13T..." } ] }