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.

internal/dto/binding.go

@@ -0,0 +1,13 @@
+package dto
+
+// BindingDTO defines inbound payload for binding creation/update.
+// It maps "(namespace, public_model)" to a RouteGroup and an upstream selector.
+type BindingDTO struct {
+	Namespace     string `json:"namespace"`
+	PublicModel   string `json:"public_model"`
+	RouteGroup    string `json:"route_group"`
+	SelectorType  string `json:"selector_type"`
+	SelectorValue string `json:"selector_value"`
+	Status        string `json:"status"`
+}
+