[P2][HR][Gaps][Toolkit][Test] Add regression test for StatusBar Background/Foreground edits #1585

Source

Sub-issue of unoplatform/private#926. Tracked from the HR/HD test matrix.

Status from matrix

Working scenario — needs regression test — verified working (HR ✅ / HD ✅ where applicable).

Scenario

Setting StatusBar.Background / StatusBar.Foreground (StatusBarExtensions) is HR- and HD-aware.

Goal

This scenario was reported as working in the manual HR/HD pass. To prevent future regressions, we need a Hot Reload regression test in the Uno.Toolkit.UI HR testharness that exercises this exact scenario by triggering the relevant edits at runtime and asserting expected post-HR behavior.

Acceptance

• Regression test added in the HR testharness covering: StatusBar.Background / StatusBar.Foreground edits
• Test runs as part of CI on the relevant platforms