Animation effects follow the operating system's setting; View ▸ Accessibility ▸ Animation Effects (#759)

With Windows set to show no animations (Settings ▸ Accessibility ▸ Visual
effects ▸ Animation effects), dialogs and menus still faded in and wheel
input glided. All of that motion is egui's default behaviour, and nothing
asked the operating system.

- crates/ui-egui/src/animation.rs: AnimationPref (System, On, Off). Off sets
  egui's animation_time to 0 and scroll_animation to none (window, menu,
  tooltip and popup fades, collapsing sections, scroll bars, scroll-to
  glides), hands each wheel notch to scroll areas whole, and lets
  Cmd/Ctrl+wheel zoom reach its zoom in one step.
- System, the default, follows the OS live: UISettings::AnimationsEnabled on
  Windows, NSWorkspace's Reduce motion on macOS, the XDG Desktop Portal's
  reduced-motion (then GNOME's enable-animations) on Linux and the BSDs,
  prefers-reduced-motion on the web.
- View ▸ Accessibility ▸ Animation Effects ▸ Use System Setting / On / Off,
  the same choice in Options ▸ Display, and `ui.animations`, `options` and
  `ui.set` {"animations"}; `ui.inspect` reports whether animations show.

Drafting behaviour is untouched: tracking's acquisition pause, the
time-sensitive right-click, previews, the caret blink, realtime pan and
zoom. Plain wheel zoom already moved a whole notch per frame (#692).

macOS and Linux are compile-checked (clippy -D warnings for
aarch64-apple-darwin and x86_64-unknown-linux-gnu), not run.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
Co-authored-by: Brandon Thomas <echelon@gmail.com>

Cargo.lock

@@ -557,9 +557,11 @@ dependencies = [
  "hidapi",
  "log",
  "muda",
+ "objc2-app-kit 0.3.2",
  "rfd",
  "serde_json",
  "sys-locale",
+ "windows",
  "winit",
  "winresource",
  "zbus",