feat(imports): add alpha Sure preflight overlay

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Summary

• Add the alpha-only Sure import preflight overlay while the pinned alpha image catches up.
• Keep the alpha template clearly separated from stable and marked as beta/testing.

What changed

• Bumped the alpha AIO revision and updated alpha docs, changelog, XML changes, and release notes.
• Added alpha overlay initializers for strict Sure import preflight and route-parity import handling.
• Added an alpha failure partial overlay that renders import errors.
• Kept merge behavior out of Unraid template and environment controls.
• Added asset and runtime regression coverage for the alpha overlay.

Why

• The alpha lane needs clear import diagnostics for dirty target data without exposing unsafe merge defaults or changing the stable package.

Validation

• python -m pytest tests/test_alpha_lane_assets.py
• python -m pytest tests/integration/test_container_runtime.py::test_alpha_image_boots_with_version_import_limits_and_webauthn_env -q
• ruby -c rootfs-alpha/rails/config/initializers/sure_aio_alpha_import_preflight.rb
• ruby -c rootfs-alpha/rails/config/initializers/sure_aio_alpha_route_parity_importer.rb
• ruby -c rootfs-alpha/rails/config/initializers/sure_aio_alpha_import_limits.rb
• erb -x -T - rootfs-alpha/rails/app/views/imports/_failure.html.erb | ruby -c
• git diff --check

Notes

• Draft PR for review and CI feedback.
• This is alpha-only and does not add a stable template control.