Add Modular Inverse operation

[p-leriche]

Description

Computes the modular multiplicative inverse of a value modulo m.

Changes

• Add ModularInverse.mjs operation
• Update Categories.json to include Modular Inverse in Crypto category

Functionality

Finds x such that: a·x ≡ 1 (mod m)

The modular inverse is essential for:

• RSA decryption and signing
• Elliptic curve cryptography
• Solving modular equations
• Diffie-Hellman key exchange

Features

• Supports decimal and hexadecimal input (0x prefix)
• Handles arbitrarily large integers using BigInt
• Uses Extended Euclidean Algorithm (iterative, no recursion limits)
• Clear error messages when inverse doesn't exist (gcd ≠ 1)
• Flexible input: can use operation args or input field

Dependencies

Depends on #2205

Testing

• Tested with coprime values (inverse exists)
• Tested with non-coprime values (proper error handling)
• Tested with crypto-grade large integers (RSA-2048 size)
• Verified: (a · inverse) mod m = 1
• Built successfully with npm run build