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/scenario/scenario-step.entity.ts

@@ -1,11 +1,11 @@
 import {
-  Entity,
-  PrimaryGeneratedColumn,
   Column,
   CreateDateColumn,
-  UpdateDateColumn,
-  ManyToOne,
+  Entity,
   JoinColumn,
+  ManyToOne,
+  PrimaryGeneratedColumn,
+  UpdateDateColumn,
 } from "typeorm";
 import { ScenarioEntity } from "./scenario.entity";