Update Qc Log Entry Placement

Edit a single qc_log batch entry's storage placement/location.

InventoryTab.js's "batches" are qc_log entries, not receiving_log entries (each QC pass gets its own qc_log[] entry with its own placement) — this is the qc_log counterpart to update_receiving_log_entry (receiving_log), letting a shop correct a placement typo'd at inspection time, or fill one in for a legacy batch that never got one, without needing to redo QC.

Body: { placement: str | null, save_as_shop_location?: bool }