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/browser/dto/exec.dto.ts

@@ -1,6 +1,5 @@
 import { ApiProperty, ApiPropertyOptional } from "@nestjs/swagger";
-import { IsObject, IsOptional, IsString, IsUrl } from "class-validator";
-import type { EnvironmentData } from "../../environment/environment.entity";
+import { IsObject, IsOptional, IsString, IsUUID, IsUrl } from "class-validator";
 
 export class ExecDto {
   @ApiPropertyOptional({
@@ -23,27 +22,27 @@ export class ExecDto {
 
   @ApiProperty({
     description:
-      "JavaScript code to execute. Receives `page` (Playwright Page) and `context` (BrowserContext) as arguments. May be async. Return value is serialised and returned.",
-    example: "return await page.title();",
+      "Async JavaScript body. Use `context.page` for Playwright, `context.getEnv(key)`, `context.getCredential(alias)`, `context.runSnippet(name, ...args)`.",
+    example: "return await context.page.title();",
   })
   @IsString()
   code: string;
 
   @ApiPropertyOptional({
     description:
-      "Key/value map of environment variables available via `helpers.env` and `helpers.getEnv()` in the script.",
-    example: { BASE_URL: "https://example.com" },
+      "UUID of an existing environment entity. Its key/value data is available via `context.env` and `context.getEnv()` in the script.",
+    example: "a6a1fca5-0f61-48ed-ae97-011dc7236387",
   })
   @IsOptional()
-  @IsObject()
-  environment?: EnvironmentData;
+  @IsUUID()
+  environmentId?: string;
 
   @ApiPropertyOptional({
     description:
-      "Key/value map of credentials available via `helpers.getCredential()` in the script.",
-    example: { admin: { username: "user", password: "pass" } },
+      "Map of alias → credential UUID. Each credential is loaded from the DB and available via `context.getCredential(alias)` in the script.",
+    example: { pkcs_key: "e3b0c442-98fc-11d8-9669-0800200c9a66" },
   })
   @IsOptional()
   @IsObject()
-  credentials?: Record<string, unknown>;
+  credentials?: Record<string, string>;
 }