Make buildID persistent for multiarch build

[alik-agaev]

Description and Related Issue(s)

This PR implements custom build ID generation in our Next.js configuration.

This should resolve the issue of having different buildIDs in Docker images built for different architectures under the same tag. That inconsistency has prevented us from scaling the frontend across both amd64 and arm64 nodes.

Proposed Changes

Support environment-based build IDs via NEXT_BUILD_ID
Provide a fallback unique ID when no env var is specified (using timestamp + random string)

Breaking or Incompatible Changes

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Additional Information

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Checklist for PR author

• I have tested these changes locally.
• I added tests to cover any new functionality, following this guide
• Whenever I fix a bug, I include a regression test to ensure that the bug does not reappear silently.
• If I have added, changed, renamed, or removed an environment variable
  • I updated the list of environment variables in the documentation
  • I made the necessary changes to the validator script according to the guide
  • I added "ENVs" label to this pull request

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