Add scientific calculator with dark/light theme toggle

[Copilot]

Transforms basic 4-function calculator into full scientific calculator with persistent theme switching.

Changes

Scientific Functions (client-side)

• Trigonometry: sin, cos, tan (degree mode)
• Logarithms: log (base 10), ln (natural)
• Powers/roots: x², x^y, √, eˣ
• Utilities: |x|, 1/x, %, ±
• Constants: π, e

Theme System

• Toggle button with localStorage persistence
• Explicit .dark-theme class replaces media query approach
• Icon switches between 🌙 (light mode) and ☀️ (dark mode)

Layout

• Expanded from 4-column to 5-column grid
• Increased size: 90vw × 95vh (from fixed 320px)
• Maintained responsive breakpoints for mobile/tablet/desktop

Implementation Notes

• Power operation (x^y) handled client-side via Math.pow()
• Basic arithmetic (+, -, ×, ÷) still uses existing server API
• Backward compatible with all existing tests

Screenshots

Before:

After - Light Mode:

After - Dark Mode:

Original prompt

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This section details on the original issue you should resolve

<issue_title>Update the calcualtor</issue_title>
<issue_description>I want to update the calculator to include

• Modern Design with dark/light mode
• A full scneitific calculator
• Ability to change theme.

Acceptance criteria:

• Screenshot of before and after.
• Test each use case
• All buttons should work
• Calcualtors cover the screen.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Update the calcualtor #26

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