Honor system reduced-motion preferences in the TUI (#44666)

## Why

The TUI should respect the host's accessibility preference even when `tui.animations` is enabled.

## What changed

- Read the system motion preference once at launch on macOS, Windows, and Linux. Changes to that preference require restarting the TUI.
- Suppress animations when reduced motion is requested without changing saved configuration. Preserve configured behavior when detection is unavailable, and limit the Linux portal query to 250 ms.
- Use the effective animation setting for voice controls and transcripts, and honor system reduced motion in the startup composer.

## Testing

Add tests for animation preference resolution and preservation of saved settings, plus composer snapshots without sparkles at widths of 40 and 80 columns.

GitOrigin-RevId: 3ea4e721ae23220a040a06123a27286a8c8f1c7c

codex-rs/Cargo.lock

@@ -4768,6 +4768,7 @@ dependencies = [
  "itertools 0.14.0",
  "lazy_static",
  "libc",
+ "objc2-app-kit",
  "pathdiff",
  "pretty_assertions",
  "pulldown-cmark",
@@ -4808,6 +4809,7 @@ dependencies = [
  "windows-sys 0.52.0",
  "winsplit",
  "wiremock",
+ "zbus",
 ]
 
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