Fix: resolve calculator logic and UI bugs [Issue]#399

[Sanjhivvarshan-b-s]

📝 Description

This PR resolves critical logic bugs and UI edge cases within the calculator.js component. I have made changes to the files and added some extra features as well.

What I Fixed:

1. Fixed the "Error" screen: The calculator now automatically resets if you try to type a new number after getting an error.
2. Fixed crashing: Stopped the calculator from breaking if you press a math button (like sin or sqrt) before finishing an equation.
3. Fixed trigonometry math: Updated sin, cos, and tan to use standard degrees instead of radians so they give the right answers.
4. Fixed display symbols: Made the screen show proper math symbols (× and ÷) instead of computer code symbols (* and /).
5. Fixed keyboard glitch: Stopped a background bug that was causing the calculator to type numbers twice when using your keyboard.

🔗 Linked Issue

Closes #399

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📋 Contribution Checklist

• My code strictly adheres to the project guidelines (Standard library only, procedural code, clean spacing).
• I have verified that my files are placed in the correct directory.
• I have tested my changes thoroughly on my local machine.
• I have included interactive emojis and clean console/UI outputs.
• GSSoC 2026: I have been formally assigned to this issue and noted it above.

[vercel]

@Sanjhivvarshan-b-s is attempting to deploy a commit to the Anuj's projects Team on Vercel.

A member of the Team first needs to authorize it.

[Sanjhivvarshan-b-s]

Hi @steam-bell-92 I've made all the changes and bug fixes and submitted the PR.