fix(console): restore incident email template preview

[dotnetpower]

Purpose

Restore the reviewed Calm Slate incident-opened email in Settings > Integrations instead of rendering placeholder markup in an unbounded full-width frame.

Changes

• package the reviewed synthetic incident-opened HTML with Operator Service and serve it from the existing preview endpoint
• center the sandboxed preview on a bounded 760 CSS pixel canvas while preserving the 640 pixel desktop email sheet
• add byte-parity, safety-boundary, package-composition, and responsive browser regressions
• keep the preview assertions in the canonical Operator Service composition suite so service test ownership remains exhaustive
• record the Console implementation transition and the unchanged Cost Governance host-seam boundary

Safety and authority

This is a read-only synthetic preview. It adds no notification delivery, approval, execution, package activation, or managed-resource authority. The iframe remains sandboxed, and the template states that approval and execution stay in the Console.

Validation

• uv run pytest -q --no-cov services/operator-service/tests/test_operator_service_composition.py - 94 passed, 1 optional PDF skip
• uv run pytest -q --no-cov tests/integration/scripts/test_service_test_suites.py - 29 passed
• npm --prefix console run test:e2e -- tests/e2e/settings-email-template-preview.spec.ts --project=desktop-chromium --workers=1 - 3 passed
• npm --prefix console run build - passed
• Operator wheel package-resource check - passed
• commit and pre-push hooks, including design, translation, document-size, and structural gates - passed

Evidence limits

The browser evidence uses the production Console shell with deterministic Operator API fixtures at 1440x900, 993x641, and 390x844. It does not claim authenticated live-stack behavior or cross-client Outlook/Gmail/Apple Mail pixel parity.

Closes #969