Guarantee the push service worker is included in release images

[Muukuro]

Motivation

• Recent image-size optimizations made including public/ assets incidental to the builder stage and risked releasing images without public/push-sw.js, breaking browser push notifications.

Description

• Copy public/ from the builder into ./.next/standalone/public in the final Docker stage and add a build-time assertion test -f ./.next/standalone/public/push-sw.js so the Docker build fails if the push service worker is missing, while preserving the reduced standalone image layout.

Testing

• Ran git diff --check and npm run lint, both succeeded; npm run build could not fully complete here because the environment could not fetch Google Fonts; and a full Docker image build could not be run because the Docker CLI is not available in this environment.

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Codex Task