fix(agent): include token in enrollment view command

[simonjcarr]

Summary

• include stored enrolment tokens in the admin token list payload under an admin guard
• build the view-existing-token install command with CT_OPS_ENROLMENT_TOKEN
• update focused authz and E2E coverage for the existing-token view command

Validation

• pnpm --dir apps/web type-check
• node apps/web/lib/actions/agents-authz.test.mjs
• node --test apps/web/lib/agent/install-script.test.mjs
• pnpm --dir apps/web test:unit
• pnpm --dir apps/web test:e2e tests/e2e/settings/agent-enrolment.spec.ts (issue-specific existing-token case passed; neighboring pre-existing failures tracked in test(web): stabilise agent enrolment E2E submit cases #1427)