refactor(api): access orchestrator through an interface

APIStore held the concrete *orchestrator.Orchestrator, which cannot be
constructed in a unit test, so handler paths that call the orchestrator
(the snapshot fallbacks in get/connect/resume) were untestable. Introduce
a sandboxOrchestrator interface (composed of focused sandboxOps and node
role interfaces) covering the methods the handlers use, and hold it on
APIStore. A compile-time assertion keeps the concrete type in sync, and
mockery generates a mock for handler tests. No behavior change.

Author: adababys

.mockery.yaml

@@ -92,3 +92,9 @@ packages:
           filename: mockfeatureflagsclient.go
           pkgname: handlersmocks
           structname: MockFeatureFlagsClient
+      sandboxOrchestrator:
+        config:
+          dir: packages/api/internal/handlers/mocks
+          filename: mocksandboxorchestrator.go
+          pkgname: handlersmocks
+          structname: MockSandboxOrchestrator