Creates a new standalone lien filing submission in a draft
state, without anchoring it to a business or person known to the
platform. Use this when the debtor has not gone through a KYB
search — all debtors are supplied manually through the debtors
list and remain fully editable while the submission is a draft.

Unlike the business- and person-anchored variants, the response
carries no assigned_debtor; every debtor lives in debtors.

Parties may be supplied incomplete while drafting. Draft values
are persisted as entered, and submit-time validation reports
anything still missing.

If the request body does not include secured parties, the system
will attempt to generate the first secured party using the
organization's lien filing preferences, if they are present in
the organization's profile.

The actual filing with the appropriate jurisdiction does not
occur at this stage; submit the draft through the
POST /lien_submissions/{filing_id}/submit endpoint.