Add modulo, square root, and power of two operators to calculator

[Copilot]

This PR implements three new mathematical operators for the calculator application as requested in the issue:

New Operators Added

1. Modulo Operator (%)

• Operation: Returns the remainder of division (a % b)
• API: GET /arithmetic?operation=modulo&operand1=X&operand2=Y
• UI: % button and keyboard % key support
• Example: 15 % 4 = 3

2. Square Root Operator (√)

• Operation: Returns the square root of operand (√a)
• API: GET /arithmetic?operation=sqrt&operand1=X
• UI: √ button (unary operation - calculates immediately)
• Example: √64 = 8

3. Power of Two Operator (x²)

• Operation: Returns operand squared (a²)
• API: GET /arithmetic?operation=power2&operand1=X
• UI: x² button (unary operation - calculates immediately)
• Example: 8² = 64

Implementation Details

Backend Changes (api/controller.js)

• Added three new operations to the operations object
• Modified validation logic to support unary operations that don't require operand2
• Maintained backward compatibility with existing binary operations

Frontend Changes (public/client.js)

• Extended switch statement to handle new operator symbols
• Implemented unary operation logic that calculates immediately when operator is pressed
• Added keyboard support for modulo operator (%)

UI Changes (public/index.html)

• Added three new operator buttons to the calculator interface
• Buttons are positioned after the existing operators for easy access

Comprehensive Testing (test/arithmetic.test.js)

• Added 12 new unit tests (4 for each operator)
• Tests cover edge cases including:
  • Positive and negative numbers
  • Zero values
  • Floating point numbers
  • Various mathematical scenarios

Quality Assurance

• ✅ All 36 tests passing (24 existing + 12 new)
• ✅ No regressions in existing functionality
• ✅ ESLint clean with no warnings
• ✅ Manual testing confirms UI functionality
• ✅ API endpoints tested and verified

Acceptance Criteria Met

• ✅ Pass unit tests for these operators
• ✅ Operators visible in the UI of the calculator

The new operators are fully functional and integrate seamlessly with the existing calculator interface and API.

Fixes #16.

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[haslam93]

clean up the UI

[haslam93]

@copilot Clean up the UI

[Copilot]

@copilot Clean up the UI

UI has been cleaned up in commit 2eee1f4. Changes include:

• Reorganized calculator buttons into a cleaner 4x6 grid layout
• Removed TODO comments and empty button elements
• Moved new operators (%, √, x²) to better positions in the layout
• Made equals button span two columns for better visual balance
• All functionality verified working correctly