Add mobile calculator example for beginners

[femmudas]

Description

Added a beginner-friendly calculator example that demonstrates basic FHE operations with clear comments and mobile-optimized output.

Features

• Simple arithmetic operations (add, subtract, multiply)
• Clear step-by-step comments for beginners
• Mobile-friendly output formatting with emojis
• Built-in test verification
• Perfect for mobile users learning FHE

Testing

• Example runs successfully
• All operations verified with assertions
• Code follows project style guidelines
• Includes test module for verification

Checklist

• Code is well-commented
• Example is easy to understand
• No breaking changes introduced
• Follows Rust best practices

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[cla-bot]

Thank you for your pull request. We require contributors to sign our Contributor License Agreement / Terms and Conditions, and we don't seem to have the users @femmudas on file. In order for us to review and merge your code, please sign:

• For individual contribution: our CLA
• for Bounty submission, if you are an individual: our T&C
• for Bounty submission, if you are a company: our T&C
  to get yourself added.

If you already signed one of this document, just wait to be added to the bot config.

[github-actions]

This PR is unverified and has been open for 2 days, it will now be closed. If you want to contribute please sign the CLA as indicated by the bot.