fix(figurecomposer): show controls for selected BZ mode

[kmnhan]

Summary

• Show the fixed kz controls only for in-plane Brillouin-zone slices.
• Show the fixed in-plane momentum control only for out-of-plane slices.
• Update the visible row immediately when the mode changes.
• Preserve both momentum values when the user switches modes.
• Restore the correct control visibility from saved operation state.

Root cause

The Brillouin-zone editor added both momentum rows without connecting their
visibility to the selected slice mode.

Validation

• QT_QPA_PLATFORM=offscreen QT_API=pyqt6 uv run pytest -q tests/interactive/imagetool/manager/figurecomposer/test_overlays.py (26 passed)
• QT_QPA_PLATFORM=offscreen QT_API=pyside6 uv run pytest -q tests/interactive/imagetool/manager/figurecomposer/test_overlays.py (26 passed)
• uv run ruff check src/erlab/interactive/_figurecomposer/_operations/_bz_overlay.py tests/interactive/imagetool/manager/figurecomposer/test_overlays.py
• uv run ruff format --check src/erlab/interactive/_figurecomposer/_operations/_bz_overlay.py tests/interactive/imagetool/manager/figurecomposer/test_overlays.py
• uv run mypy src/erlab/interactive/_figurecomposer/_operations/_bz_overlay.py
• git diff --check

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.93%. Comparing base (40f973f) to head (44bd08a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #553      +/-   ##
==========================================
- Coverage   91.94%   91.93%   -0.01%     
==========================================
  Files         250      250              
  Lines       98809    98821      +12     
  Branches    16610    16610              
==========================================
+ Hits        90845    90854       +9     
- Misses       4576     4577       +1     
- Partials     3388     3390       +2     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.