Avalonia UI: refine navigation, search boxes, filter pane & operation banners

[Gabriel Dufresne (GabrielDuf)]

Addresses users feedback on the Avalonia UI, bringing several interactions closer to the WinUI app and smoothing out the animations.

Navigation panel

• Replaced the single width sidebar with a WinUI NavigationView-style layout: a static icon rail plus a labeled flyout that cross-fades in over the content (GPU-composited, so the package list never reflows during the transition).
• Rail and flyout are one SidebarView bound to the same view-model (new ShowLabels property), so selection, badges and loading stay in sync.
• Fixed 64px rail so loading bars/badges can't inflate it; loading indicator is a small bar centered under the icon.
• Transparent light-dismiss, collapse-on-navigate, and a title-bar back button wired to the existing back-navigation.
• Thinner, more Fluent hamburger glyph.

Search boxes (top bar + Discover mega query)

• WinUI-style focus treatment: a single accent underline across the whole box (field + button) instead of recoloring the entire border.
• The field keeps the container fill in every state (no black background swap on focus), so field and button stay one consistent color.
• Hover shows a subtle neutral underline; focus switches it to the accent color.
• Top box: subtler corner radius and a small left nudge to match WinUI placement.

Filter pane

• Opening/closing now slides on a compositor RenderTransform (clipped by the panel) instead of width-tweening the column, which reflowed the package list every frame and felt laggy. The list resizes once up front so the pane never sits beside an empty gap.
• Toolbar buttons keep sliding via their MinWidthtransition.

Operations

• Dropped the redundant in-app success banner — the operations panel already shows the completed status. OS toasts and accessibility announcements are unchanged; failures still surface a banner.

[Gabriel Dufresne (GabrielDuf)]

Hi TonyBlu (@TonyBlur), just letting you know that I've added the few recommendations you mentioned the other day. Thanks for the feedback!