10228 Provider Model Delete Tombstones Synced Sibling - Omniroute

fix(api): deleting a manually-added custom model no longer tombstones a provider-synced model that shares its id. DELETE /api/provider-models is addressed by provider + model alone, so when both a custom row and a synced row existed for one id it removed both and wrote isDeleted:true. replaceSyncedAvailableModelsForConnection then filtered that id out of every subsequent re-import, so the provider could never resync — model sync kept reporting added: N while the catalog stayed empty and /v1/models never listed the model again, even though routing to it still worked. The custom row is now removed first and its presence is treated as the operator's intent, leaving the synced sibling importable; a synced-only delete still tombstones as before (#3199, #3782 unaffected) (#10228) — thanks @Neuron-Mr-White