Partial-update payload for an existing order.

table_id distinguishes "omitted" from an explicit null: sending null
DETACHES the order from its table, which is how the app frees a table it had
seated. Callers must therefore check model_fields_set, not just the value —
both cases read as None.

Deliberately carries no claimed_offer_total. Offers still re-derive on this
path (it funnels through the same totals seam) and still evaluate at the order's
original sale instant, so an edit cannot silently reprice a closed happy hour.
What is skipped is the claim check: this endpoint replaces line items, a second
claim protocol would double the surface, and no product flow needs it yet.