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

client/src/pages/scenario/ScenarioDetailPage.tsx

@@ -1,4 +1,4 @@
-import { useEffect, useState, SubmitEvent } from 'react';
+import { useEffect, useRef, useState, SubmitEvent } from 'react';
 import { useNavigate, useParams } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import {
@@ -68,6 +68,7 @@ export function ScenarioDetailPage() {
   const [saveSessionFlag, setSaveSessionFlag] = useState(false);
   const [envs, setEnvs] = useState<Environment[]>([]);
   const [selectedEnvId, setSelectedEnvId] = useState('');
+  const envInitRef = useRef(false);
   const [pendingDelete, setPendingDelete] = useState<
     { type: 'scenario' } | { type: 'step'; id: string } | { type: 'credential'; id: string } | null
   >(null);
@@ -90,11 +91,19 @@ export function ScenarioDetailPage() {
       .list(1, 200)
       .then((r) => {
         setEnvs(r.data);
-        setSelectedEnvId((prev) => prev || r.data[0]?.id || '');
       })
       .catch(() => {});
   }, [id]);
 
+  // Default selected env to scenario's linked environment (or first env) once both are loaded
+  useEffect(() => {
+    if (envInitRef.current || envs.length === 0) return;
+    envInitRef.current = true;
+    const preferred = scenario?.environmentId ?? null;
+    const exists = preferred ? envs.some((e) => e.id === preferred) : false;
+    setSelectedEnvId(exists ? preferred! : envs[0].id);
+  }, [scenario, envs]);
+
   const reloadScenario = async () => {
     if (!id) return;
     const s = await scenarios.get(id);
@@ -389,6 +398,19 @@ export function ScenarioDetailPage() {
               items={[
                 { term: t('scenarios.field_id'), detail: <UuidBadge id={scenario.id} /> },
                 { term: t('scenarios.field_name'), detail: scenario.name },
+                ...(scenario.environment
+                  ? [{
+                      term: t('scenarios.field_environment'),
+                      detail: (
+                        <a
+                          href={`/environments/${scenario.environment.id}`}
+                          onClick={(e) => { e.preventDefault(); navigate(`/environments/${scenario.environment!.id}`); }}
+                        >
+                          {scenario.environment.name}
+                        </a>
+                      ),
+                    }]
+                  : []),
                 {
                   term: t('scenarios.field_created'),
                   detail: <Timestamp value={scenario.createdAt} />,