Upgrade Calculator Fabric Apps to React Native Windows 0.80.x dependencies

[Copilot]

This PR upgrades the CalculatorExperimental sample to use React Native Windows 0.80.x dependencies while maintaining minimal changes to preserve the existing structure, GUIDs, and functionality.

Changes Made

Dependency Updates

• React Native: 0.79.3 → 0.80.2 (latest stable)
• react-native-windows: 0.79.0 → 0.80.0-preview.3 (latest 0.80.x preview)
• React: 19.0.0 → ^19.1.0 (satisfies peer dependency requirements)
• @react-native-community/cli: 18.0.0 → 20.0.1 (latest)
• All @react-native/ packages*: Updated to 0.80.2 for consistency

Documentation Updates

• Updated README.md to reflect that the sample now targets RNW 0.80

Verification

The upgrade has been thoroughly tested to ensure compatibility:

• ✅ All linting passes with no errors
• ✅ All tests pass (both regular and Windows-specific)
• ✅ Metro bundler starts correctly with React Native v0.80
• ✅ JavaScript bundle generates successfully for Windows platform
• ✅ Fabric configuration preserved (RnwNewArch=true in ExperimentalFeatures.props)
• ✅ Package.appxmanifest maintains correct publisher "CN=React Native Windows Sample"
• ✅ All GUIDs and solution files remain unchanged
• ✅ Calculator functionality (App.tsx) fully preserved

Benefits

This upgrade brings the CalculatorExperimental sample up to date with the latest React Native Windows 0.80.x releases, ensuring developers have access to the latest features, performance improvements, and bug fixes while maintaining the experimental Fabric rendering system compatibility.

The minimal-change approach preserves all existing configuration and ensures a smooth transition without breaking existing workflows or requiring manual GUID restoration.

Fixes #1076.

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