Canteen Management

Done. GET /api/canteen/dietary/orders + portal list page at /dietary/orders,
linking each row into the existing [orderId] review screen with the
admission id prefilled. Added "Diet orders" to the Dietary nav group.

Found and fixed a real bug along the way: IDietaryOrderReadContract (D22's
local placeholder) had no DI registration, so DietOrderSyncService failed
to construct at all -- this was silently crashing DietOrderPollJob in the
background every poll cycle already. Added a local stub (same pattern as
D25's admission one) so the service builds; only the actual IPD sync calls
throw until the real contract lands.

Backend: 4 new tests green, full suite 783/785 (2 pre-existing unrelated
failures). Portal: type-check clean, 472/472 tests green. Pushed to
integration/canteen-v1 (baa27d5).