feat(api): add admin endpoints for binding management

Implement handlers for creating, listing, and updating model bindings.
Register new routes in the admin server group and add DTO definitions.
Update provider handlers to trigger binding synchronization on changes
to ensure upstream mappings remain current.

cmd/server/main.go

@@ -167,6 +167,9 @@ func main() {
 		adminGroup.POST("/models", handler.CreateModel)
 		adminGroup.GET("/models", handler.ListModels)
 		adminGroup.PUT("/models/:id", handler.UpdateModel)
+		adminGroup.POST("/bindings", handler.CreateBinding)
+		adminGroup.GET("/bindings", handler.ListBindings)
+		adminGroup.PUT("/bindings/:id", handler.UpdateBinding)
 		adminGroup.POST("/sync/snapshot", handler.SyncSnapshot)
 	}