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

server/src/scenario/scenario.service.ts

@@ -410,6 +410,7 @@ export class ScenarioService {
       kind: "scenario",
       id: scenario.id,
       name: scenario.name,
+      description: scenario.description ?? undefined,
       steps: scenario.steps.map((s) => ({
         title: s.title,
         execCode: s.execCode,
@@ -424,17 +425,25 @@ export class ScenarioService {
       const existing = await this.scenarioRepo.findOneBy({ id: dto.id });
       if (existing) {
         existing.name = dto.name;
+        existing.description = dto.description ?? null;
         scenario = await this.scenarioRepo.save(existing);
         // Delete old steps and recreate
         await this.stepRepo.delete({ scenarioId: scenario.id });
       } else {
         scenario = await this.scenarioRepo.save(
-          this.scenarioRepo.create({ id: dto.id, name: dto.name }),
+          this.scenarioRepo.create({
+            id: dto.id,
+            name: dto.name,
+            description: dto.description ?? null,
+          }),
         );
       }
     } else {
       scenario = await this.scenarioRepo.save(
-        this.scenarioRepo.create({ name: dto.name }),
+        this.scenarioRepo.create({
+          name: dto.name,
+          description: dto.description ?? null,
+        }),
       );
     }
     if (dto.steps.length > 0) {