## Problem
`POST /superuser/invoicing/period/tree-actions/preview` could return
`409 Invoice-period snapshot is missing or expired` during normal UI
flows when a snapshot binding aged out before the user triggered the
action.
## Fix
- introduce a dedicated snapshot cache TTL
(`SNAPSHOT_BINDING_TTL_SECONDS`)
- keep preview cache TTL unchanged (`PREVIEW_TTL_SECONDS`)
- use the longer snapshot TTL for actor/customer snapshot binding writes
This preserves existing safety because snapshot bindings are still
revalidated against fresh revision data before use.
## Tests
- `vendor/bin/pest
tests/Unit/Invoicing/InvoiceCollectionBulkActionSafetyTest.php
--colors=never`
- `vendor/bin/pest tests/Api/CollectedInvoiceBulkActionsApiTest.php
--colors=never` (suite present; skipped without `RUN_API_TESTS=1`)
Co-authored-by: Jeppe Bundgaard <jb@truckwash.dk>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
