Hosts SettingsDrawer in the main content grid as a fixed-width 400px
panel positioned at the right edge, with a TranslateTransform pre-set
to X=400 so it starts off-screen. The rail's settings icon triggers a
220ms ease-out-quart slide-in storyboard; CloseRequested (or the
drawer's Esc/close button) triggers a 180ms ease-in slide-out.
IsHitTestVisible toggles in sync so the off-screen drawer doesn't
intercept clicks on the participants list.
This is the structural commitment from DESIGN.md: settings live in a
right-drawer (not a permanent 380px panel), the participants table
reclaims full width when settings aren't being edited.
Builds clean.
Followup: tab content currently rebuilds imperatively in code-behind;
wire it to a SettingsViewModel mirror of the WPF host's
GlobalSettingsViewModel once the view-model migration starts (Phase 4
of the migration plan).
Zac Gaetano
2909d8b1d7