chore: AUT-1599 bump nightly Megatron Core pins

[svcnemo-autobot]

Background

Validate Bridge against frozen MCore main 731b791469004f8fdcb896e65d610d6b1b0ebb32 and dev 2f2f8ebaef90f4d62a18a43808398223b1fc5809.

Only this PR may merge after both lanes prove compatibility commit d4409c8593b54a5b4d64c54327ebce02bc6ad184. The dev PR #5709 is validation-only.

What changed

• Updated both commit files and pinned the gitlink to MCore main.
• Added shared uv dependency metadata for source-only lock resolution.
• Disabled TransformerEngine recursive build-time submodule fetching and added a regression gate.
• Retained the independently generated main lock.

Details

flowchart LR
  C[shared compatibility d4409c85] --> M[main landing lane]
  C --> D[dev validation lane]
  D -. must pass .-> M

Loading

Tested

• Both lane dependency-layer gates pass, including inherited TE source parity and the no-recursive-fetch invariant.
• Frozen commit files and lane gitlinks verified.
• Fresh exact-head image build and paired local validation are in progress.

[copy-pr-bot]

This pull request requires additional validation before any workflows can run on NVIDIA's runners.

Pull request vetters can view their responsibilities here.

Contributors can view more details about this message here.

[svcnvidia-nemo-ci]

/ok to test 92f0ca7