Implements the shared validateSchedule validator (daily + weekly, midnight
spillover, Sunday->Monday wrap, adjacency, empty-block rejection), a
per-License-Key schedule service (get/set type, CRUD blocks, weekly
prefill with confirmation), the content-hash version/ETag serializer, the
new GET /api/v2/licenses/[licenseKey]/schedule (200/304/404, type null),
and additive evolution of the legacy GET /api/v2/schedule. Adds validator,
serializer (against docs/fixtures), endpoint ETag/304, and service tests.
