feat(scenarios): link scenarios to a default environment

- add optional ManyToOne relation from scenario to environment entity
- expose environmentId in create/update DTOs, service, and MCP tools
- pre-select linked environment in run modals on detail and list pages
- add environment selector to create/edit scenario forms
- show linked environment as a navigable link on scenario detail page

server/src/scenario/scenario.service.ts

@@ -77,6 +77,7 @@ export class ScenarioService {
         "steps",
         "scenarioCredentials",
         "scenarioCredentials.credential",
+        "environment",
       ],
       order: { steps: { order: "ASC" } },
     });