feat(snippets): add snippets entity, crud, and auto-browser-per-run

- add Snippet entity with name, description, code; full CRUD backend
- add snippets pages (list, create, edit, detail) and nav entry
- add runSnippet helper in code-executor using new Function with args array
- add result param to execute() so validateCode can access exec output
- remove sessionName from steps; each run now spawns its own fresh browser
- fix waitForURL race by polling localStorage for token instead

server/src/app.module.ts

@@ -19,6 +19,8 @@ import { ScenarioRunStepEntity } from "./scenario/scenario-run-step.entity";
 import { ScenarioRunLogEntity } from "./scenario/scenario-run-log.entity";
 import { ScenarioCredentialEntity } from "./scenario/scenario-credential.entity";
 import { ScenarioModule } from "./scenario/scenario.module";
+import { SnippetEntity } from "./snippet/snippet.entity";
+import { SnippetModule } from "./snippet/snippet.module";
 
 @Module({
   imports: [
@@ -43,6 +45,7 @@ import { ScenarioModule } from "./scenario/scenario.module";
           ScenarioRunStepEntity,
           ScenarioRunLogEntity,
           ScenarioCredentialEntity,
+          SnippetEntity,
         ],
         synchronize: true,
       }),
@@ -52,6 +55,7 @@ import { ScenarioModule } from "./scenario/scenario.module";
     EnvironmentModule,
     CredentialModule,
     ScenarioModule,
+    SnippetModule,
     McpModule,
     HealthModule,
   ],