Fix a `tokens_value_key` unique-constraint violation in the archive node when a custom token that already exists with an owner is re-added as ownerless. This happened at archive startup with `--config-file`, where `add_genesis_accounts` re-inserts tokens without populating `Token_owners`: the owner-`IS NULL` lookup missed the existing owned row and the follow-up `INSERT` crashed the process (`Could not add batch of genesis account`), blocking block ingestion. The no-owner insertion path now looks up the token by value alone and reuses the existing row, making genesis/ownerless re-insertion idempotent.
