Gateway startup now includes plugin owners for explicit memorySearch.provider and memorySearch.fallback values, including custom models.providers API owners and generic embedding provider contracts.
Sentinel and disabled paths keep existing startup behavior for auto, local, none, disabled memory search, and disabled memory slots.
Adds post-runtime-load diagnostics for configured memory embedding providers that remain unregistered.
Closes#89651
Co-authored-by: Joseph Krug <5925937+joeykrug@users.noreply.github.com>
