android: fix system navigation bar overlay color

[yedidyak]

Summary

• Fix Android system navigation-bar overlay color initialization so the manual nav-bar background starts from the current window/resolved color instead of hardcoded black.
• Keep the manual nav-bar background in sync whenever setNavigationBarBackgroundColor(...) is called, including non-edge-to-edge mode.
• Add Robolectric coverage for initial overlay color, non-edge-to-edge window/view updates, and edge-to-edge view/icon updates.

Validation

• git diff --check — PASS
• Pre-PR self-review — PASS; no safe autofixes applied, no sensitive files found

Not Run

• yarn install — blocked in Yarn fetch step by repeated RequestError EBADF; node_modules/@react-native/gradle-plugin was not installed
• cd playground/android && ./gradlew :react-native-navigation:testDebugUnitTest --tests com.reactnativenavigation.utils.SystemUiUtilsTest — blocked because node_modules/@react-native/gradle-plugin is missing

Risks

• Low-to-medium: scoped to Android system bar color handling, but affects both edge-to-edge and non-edge-to-edge navigation-bar coloring.
• Explicit navigationBar.backgroundColor should still win; bottom-tabs sync remains unchanged.

Review Context

• WOAINFRA-3349 reports black OS navigation/gesture area under otherwise light app UI.
• The likely regression was the manual nav-bar background view being initialized to black and not repainted outside edge-to-edge mode.
• This fix does not change public JS APIs or app resource behavior.

Suggested Reviewers

• @markdevocht — dominant/latest relevant editor for the Android system-bar code touched here.