Allow updating display name for __root__ reference node

Hi, At the moment, the display name for the `__root__` reference node in Nextclade cannot be customized. Would it be possible to allow a custom display name for the default root node, similar to how other drop-down options can have `displayName` and `description` fields? This would help keep things clear and consistent, especially for custom datasets where the root reference may be less common. Having the option to define `displayName` (and optionally `description`) for `__root__` in the auspice config would be very useful. Thanks for considering it! *Example JSON config:* ``` { "ref_nodes": { "default": "__root__", ---> "displayName": "Accession ID" "search": [ { "name": "JN.1", "displayName": "JN.1 (24A)", "description": "Variant recommended for the 2024/2025 COVID-19 vaccine", "criteria": [ { "qry": [ { "clade": ["23I", "24A", "24B", "24C", "recombinant"] } ], "node": [ { "name": ["JN.1"] } ] } ] } ] } } ```