test(e2e): add agent v2 test infrastructure

[lyzno1]

Summary

• Enable Agent v2 in the E2E web environment.
• Add Agent v2 API helpers for roster agent setup, cleanup, composer draft sync, build draft operations, publish, Web app access, Backend API access, and API keys.
• Add scenario state and cleanup support for Agent v2 resources.
• Add an Agent v2 configure-page infrastructure probe scenario and step definitions.
• Document Agent v2 E2E organization and helper ownership in the E2E package guide.

Validation

• pnpm -C e2e exec eslint .
• pnpm -C e2e type-check
• pnpm -C e2e exec tsx ./node_modules/@cucumber/cucumber/bin/cucumber.js --config ./cucumber.config.ts --dry-run --tags @agent-v2
• git diff --check

Full browser E2E was not run in this pass because the full backend/frontend/middleware stack was not started.