Temporary: validate Accord Marimo notebook

[nightly]

Temporary validation harness for the exact merged nightly/accord Stage-4 data explorer notebook.

Runs:

uv run --project validation/accord-marimo marimo check --strict \
  validation/accord-marimo/data_explorer_mo.py

This PR will be closed and its branch reset after the check result is captured. It does not target any scs application change.

[nightly]

Validation completed successfully.

• Workflow run: 32678855088
• Job: 97291828857
• Python: CPython 3.12.3
• Marimo: 0.24.0
• Command:

uv run --project validation/accord-marimo marimo check --strict \
  validation/accord-marimo/data_explorer_mo.py

The checked file is byte-for-byte the merged 94-line nightly/accord:notebooks/data_explorer_mo.py content used for PR #3. The temporary branch will now be reset to master.

[nightly]

Correction: the first validation used the earlier PR #3 notebook revision captured before subsequent main updates. Its structure was equivalent, but it was not byte-for-byte identical to the current nightly/accord blob. I am reopening this temporary harness and rerunning the exact current blob 2bb35eb143519b3ad0c9341ff8efff8142287aa7; the final result will supersede the prior comment.