phsl / new-api

* feat: add upstream model update detection with scheduled sync and manual apply flows

* feat: support upstream model removal sync and selectable deletes in update modal

* feat: add detect-only upstream updates and show compact +/- model badges

* feat: improve upstream model update UX

* feat: improve upstream model update UX

* fix: respect model_mapping in upstream update detection

* feat: improve upstream update modal to prevent missed add/remove actions

* feat: add admin upstream model update notifications with digest and truncation

* fix: avoid repeated partial-submit confirmation in upstream update modal

* feat: improve ui/ux

* feat: suppress upstream update alerts for unchanged channel-count within 24h

* fix: submit upstream update choices even when no models are selected

* feat: improve upstream model update flow and split frontend updater

* fix merge conflict