Fix MultiphaseOptim notebook integrity

[EvenSol]

Summary

• remove the accidental empty code cell appended to notebooks/process/MultiphaseOptim.ipynb
• restore the notebook's existing 21-code-cell maintenance-ledger contract
• preserve every executed calculation, output, equation, table, figure, reference, and engineering conclusion

Root cause

Google Colab added a 22nd blank code cell with no execution count. Because the maintenance ledger correctly marks the notebook as passed with 21 executed code cells, the repository-wide integrity workflow failed with:

• ledger records 21 code cells, notebook has 22
• ledger says passed but execution counts are missing for code cells [22]

The stray cell contains no source and no output, so removing it is the smallest correct repair.

Validation

Base: 7848628fe0c74b36e7318e163cfbd2f809fb9071
Head: df756b64aa4dd88c2875c3d7937c3a53737af3d2

• git diff --check — passed
• python -m unittest discover -s scripts -p 'test_check_notebook.py' — 6/6 passed
• python scripts/check_notebook.py notebooks/process/MultiphaseOptim.ipynb --quiet-warnings — 0 errors, 0 warnings
• python scripts/check_notebook.py --all --quiet-warnings — 337 notebooks, 0 errors, 43 non-blocking pre-existing warnings
• clean isolated re-execution of the exact repaired notebook source — 21/21 cells completed in order, counts 1–21, zero stored exceptions, zero stderr
• validation runtime — NeqSim 3.18.0, Python 3.12.13, OpenJDK 17.0.20
• engineering validation — all 32 assertions passed; 7 connected unit operations; separator feed and products both 68.5586182 kg/s; residual -4.547e-12 kg/s
• visual validation — Colab-compatible HTML generated; a 33-page XeLaTeX rendering was inspected page by page, covering all equations, tables, and five stored figures; labels, legends, units, equations, contrast, and layout were readable with no clipping or broken visual
• repository has no .pre-commit-config.yaml; the current pull-request workflow and direct repository checks above were inspected and run

Documentation impact

Documentation impact: none. This removes only an accidental empty cell and changes no public API, installation path, model behavior, input, output, unit, assumption, default, compatibility contract, catalog entry, or user-facing guidance.

Publication state

Draft PR. GitHub Notebook integrity run 142 passed on the published head, the PR is mergeable, and no merge or auto-merge was requested.