Org policy JSON responses never included a revisionDate field, unlike
every other synced entity. The official Bitwarden server always sets
it, and current official clients (recently migrated to the WASM SDK's
typed PolicyView) now assume it is always a valid date string. Its
absence deserializes to undefined client-side, which then throws
(RangeError: Invalid time value) when the client formats it, breaking
the whole policy sync pipeline and silently emptying the vault view in
the browser and desktop apps.
Adds a revision_date column (mirroring the existing pattern used by
Send), stamped on creation and bumped on every save.