feat(scenarios,environments): add markdown description field

- add optional description to scenario and environment entities
- expose description in create/update DTOs, MCP tools, and export DTOs
- render description as markdown on detail pages
- add description editor (CodeEditor) to create/edit forms for both resources

client/src/pages/scenario/CreateScenarioPage.tsx

@@ -3,7 +3,7 @@ import { useNavigate } from 'react-router-dom';
 import { useTranslation } from 'react-i18next';
 import { X, Save, ClipboardList } from 'lucide-react';
 import { scenarios } from '../../api';
-import { Breadcrumbs, Button, Card, Input, useToast } from '../../ui';
+import { Breadcrumbs, Button, Card, Input, CodeEditor, useToast } from '../../ui';
 import styles from '../Page.module.css';
 
 export function CreateScenarioPage() {
@@ -12,6 +12,7 @@ export function CreateScenarioPage() {
   const toast = useToast();
 
   const [name, setName] = useState('');
+  const [description, setDescription] = useState('');
   const [nameError, setNameError] = useState('');
   const [saving, setSaving] = useState(false);
 
@@ -23,7 +24,7 @@ export function CreateScenarioPage() {
     }
     setSaving(true);
     try {
-      const scenario = await scenarios.create(name.trim());
+      const scenario = await scenarios.create(name.trim(), description.trim() || undefined);
       toast.success(t('scenarios.created'));
       navigate(`/scenarios/${scenario.id}`);
     } catch (err) {
@@ -64,6 +65,15 @@ export function CreateScenarioPage() {
               required
               autoFocus
             />
+            <div className={styles.formField}>
+              <label className={styles.fieldLabel}>{t('scenarios.form_description')}</label>
+              <CodeEditor
+                language="markdown"
+                value={description}
+                onChange={setDescription}
+                rows={8}
+              />
+            </div>
           </div>
 
           <div className={styles.formActions}>