[Fix] Incomplete standalone images pass pre-merge checks

[roomote-roomote]

​Opened on behalf of @mrubens. Follow up by mentioning @roomote-roomote, in the web UI, or in Slack.

What changed

• Added a final-image build check that loads every configured web server external from each standalone package copy.
• Fails the existing pre-merge Docker build when Next.js omits any direct package or transitive runtime dependency.

Why this change was made

PR #1898 fixed the incomplete standalone image, and the subsequent publish and deployment-acceptance workflow passed. The same defect could still recur undetected because pull-request CI only built the image; it did not load the externalized server packages that failed on the first request.

Impact

Incomplete standalone images now fail during pull-request Docker Build instead of after merge during deployment acceptance. A clean production web build, equivalent ESM/CJS-aware resolution of all six configured externals, web typecheck, web lint, and the full pre-push suite passed. The sandbox does not expose a Docker socket, so the pull-request Docker Build is the final check of the new image-layer command.

[roomote-community]

No code issues found. See task

• Validate every configured web server external; pino and postgres are not loaded by .docker/app/Dockerfile:387.
• .docker/app/Dockerfile:387 imports BullMQ's ESM module entry by file URL, so native Node ESM resolution fails before the final image is built.

_{Reviewed 033587d}