feat(planning-service): expose planning filter APIs used by the planning interface
Add and align the planning endpoints consumed by the UI filter layer:
- POST /api/planning/drivers/trips/filtered for driver UUID + criteria filtering
- GET /api/planning/drivers/assigned-uuids?date=... for unassigned-driver logic
- POST /api/planning/drivers/trips/by-drivers/by-uuid for date-based driver slots retrieval
Ensure endpoint contracts match frontend planning filters (date, driver UUIDs, and typed criteria).