feat(browser,mcp): resolve environment and credentials from DB in exec

- POST /exec now accepts environmentId (UUID) and credentials (alias → UUID)
  instead of raw payloads; resolves entities via EnvironmentService and
  CredentialService before passing data to browserService.exec
- exec_code MCP tool updated with same schema: environmentId + credentials map
- CredentialModule imported into BrowserModule and McpModule
- docs(scenario): rewrite script runtime section for single context argument
- docs(mcp): update exec_code description to reflect new parameter shapes
- style: reorder imports across server source (formatter)

server/src/credential/credential.module.ts

@@ -1,8 +1,8 @@
 import { Module } from "@nestjs/common";
 import { TypeOrmModule } from "@nestjs/typeorm";
+import { CredentialController } from "./credential.controller";
 import { CredentialEntity } from "./credential.entity";
 import { CredentialService } from "./credential.service";
-import { CredentialController } from "./credential.controller";
 
 @Module({
   imports: [TypeOrmModule.forFeature([CredentialEntity])],