OpenUpgrade migrations can delete and recreate ``ir_actions`` records with
new ids, leaving ``ir_filters.action_id`` (custom user filters) pointing to
a now-missing action. Opening the custom filters list then fails with
"Record does not exist or has been deleted (ir.actions.actions(<id>,))"
when Odoo resolves the ``action_id`` many2one ``display_name``.
Detach such filters (set ``action_id = NULL``) as a final, version-agnostic
cleanup step: the filter stays usable, only the broken action link is
dropped. Placed in ``finalize_db.sh`` so the check runs whatever the target
version, with an integrated re-count that warns if orphans remain.
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