TIMUIKitChat 设置 customAppBar 后，UI跑板 #75
Description
TIMUIKitChat 设置一个 customAppBar后，底部的输入框部分跑板：
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[✓] Flutter (Channel stable, 3.38.4, on macOS 26.0.1 25A362 darwin-arm64, locale
zh-Hans-CN)
[✓] Android toolchain - develop for Android devices (Android SDK version 36.1.0)
[✓] Xcode - develop for iOS and macOS (Xcode 26.0.1)
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[✓] Connected device (3 available)
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