feat(floating-pet): add an extra-large mascot size

[F21HGG]

Summary

• Add an extraLarge floating-pet size mode at a fixed 1.75x scale.
• Preserve the existing automatic, standard, and large behavior.
• Update the settings preview, English and Simplified Chinese copy, persistence coverage, scale clamping, and layout metrics tests.

Why

On built-in MacBook displays, large currently resolves to 1.16x, leaving a narrow practical size range. The new mode provides a clearly larger option without changing existing preferences.

Testing

• Fork PR Checks: passing run
  • Prototype tests
  • Xcode unit tests
• swift build --package-path Prototype
• Swift parse and focused type-check for the changed sizing declarations
• plutil -lint for both localization catalogs

Closes #294