TransactionsController#create looked up the account with
accessible_accounts.find(params.dig(:entry, :account_id)). With no
account selected the id is blank, find raises RecordNotFound, and
StoreLocation's rescue_from turns that into head :not_found — the 404
on /transactions the reporter saw.
Switch to find_by(id:) and, when it returns nil, rebuild the entry,
run validation, and re-render :new with 422, matching the existing
validation-failure branch. This covers a blank, missing, or invalid
account_id, so the user gets the form back with errors instead of a
dead button.
Fixes#2566
Co-authored-by: agentloop <agentloop@localhost>
