Feature/viewer layout

[cpignedoli]

Summary

This PR builds on #745 and focuses on improving the usability/layout of the structure viewer controls.

Depends on #745.

Changes

• Makes StructureManagerWidget use a full-width structure viewer by default, with the detailed viewer controls collapsed below the geometry.
• Adds a Below / Side controls layout switch in the Appearance tab.
• Keeps high-frequency controls visible in a compact toolbar:
  • center atoms
  • default view
  • view scale
  • show axes
  • center axes
• Uses icon-only buttons for center/default view to reduce toolbar space.
• Moves detailed scale/control explanations into the optional Show view help text.
• Removes duplicate geometry controls from the below-layout Appearance tab.
• Adds tests for the below-controls layout and compact toolbar structure.

Validation

• python -m ruff format aiidalab_widgets_base/viewers.py aiidalab_widgets_base/structures.py tests/test_viewers.py
• python -m ruff check aiidalab_widgets_base/viewers.py aiidalab_widgets_base/structures.py tests/test_viewers.py
• python -m compileall aiidalab_widgets_base/viewers.py aiidalab_widgets_base/structures.py tests/test_viewers.py
• Direct widget smoke test for the compact toolbar and Below / Side switching

Full pytest could not be run locally because the existing AiiDA/pgtest setup tries to call the missing locate executable while searching for pg_ctl before the test body starts.

Screen.Recording.2026-05-19.at.10.44.11.mov

[codecov]

Codecov Report

❌ Patch coverage is 95.58824% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.23%. Comparing base (42bcd52) to head (8684733).

Files with missing lines	Patch %	Lines
aiidalab_widgets_base/viewers.py	95.52%	3 Missing ⚠️

Additional details and impacted files

@@                    Coverage Diff                     @@
##           feature/viewercontrols     #747      +/-   ##
==========================================================
+ Coverage                   85.12%   85.23%   +0.10%     
==========================================================
  Files                          18       18              
  Lines                        3421     3514      +93     
==========================================================
+ Hits                         2912     2995      +83     
- Misses                        509      519      +10     

Flag	Coverage Δ
python-3.12	85.20% <95.58%> (+0.10%)	⬆️
python-3.9	85.21% <95.58%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[cpignedoli]

I will fix pan functionality after merging of #742