Reproducer for #57836: Fabric dynamic border/outline colors resolve against the system appearance

[JacquesLeupin]

Summary

Runnable reproducer for #57836 — on Fabric, borderColor/outlineColor set from a dynamic color (PlatformColor / DynamicColorIOS) resolve against the system appearance and ignore overrideUserInterfaceStyle. Edits only RNTesterPlayground.js; not intended to be merged.

How to run

1. Set the iOS Simulator's System Appearance to Light.
2. Run RNTester on iOS (New Architecture) and open the Playground example.
3. The demo forces the app dark via Appearance.setColorScheme('dark') at 2s and mounts a second row of boxes at 4s; a button resets to the system scheme and re-runs.

One DynamicColorIOS({light: red, dark: green}) feeds every fill and border; the two bordered boxes cover both border code paths (border-image, and CoreAnimation layer.borderColor via overflow: 'hidden').

Expected: once useColorScheme() reports dark, every fill and border is green.

Actual: fills turn green, but row A's borders (mounted before the override) stay red — the light variant — on both border paths, and persist indefinitely. Freshly-created views in row B can heal via the attach-time trait change; recycled views in real apps reattach with unchanged traits and stick like row A.

Fix proposed in #57837.

Changelog

[INTERNAL] - Reproducer for #57836, not for merge

[JacquesLeupin]

Moving the reproducer to a fork branch per our workflow — runnable single-file reproducer lives at https://github.com/JacquesLeupin/react-native/tree/repro/fabric-border-trait-collection-57836 (diff: main...JacquesLeupin:react-native:repro/fabric-border-trait-collection-57836), linked from #57836.

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