MainWindow persists preferences (window layout, canvas backend) through
QSettings("OTKO", "OTKO"), so tests constructing it were reading the
developer's real settings: after switching to the Plotly backend the
PyVista-specific viewport-axis tests failed with "PlotlyCanvas has no
attribute renderer". A session fixture now redirects QSettings into a
temp dir and is skipped when Qt is not installed, keeping the headless
job Qt-free.
Catch-all for the intermixed residue of the unpushed otko-development
work ported into this tree: combinations/console-dock/quick-guide wiring
across commands, core, services, views and tests; repo-wide ruff-format
normalization; README/CONTRIBUTING updates; and the toolbar default
(both toolbars now open in the top area, quick guide text updated).
Splitting this further would require hunk-level surgery with low
confidence; the preceding commits in this branch isolate the
self-contained features.
