Fix: Support negative parameters in Affine Cipher operations

[ThanatosXingYu]

Problem

The Affine Cipher encrypt/decrypt operations were restricted to positive integers only for parameters a and b, preventing correct decryption of ciphertexts that require negative parameters.

Example:

• Input: szzyfimhyzd
• Parameters: a=17, b=-8
• Expected output: affineshift
• Actual output: Error ”a and b must be integers“

Solution

Modified the parameter validation regex in src\core\lib\Ciphers.mjs:31 to accept both positive and negative integers:

Before:

if (!/^\+?(0|[1-9]\d*)$/.test(a) || !/^\+?(0|[1-9]\d*)$/.test(b)) {

After:

if (!/^[+-]?(0|[1-9]\d*)$/.test(a) || !/^[+-]?(0|[1-9]\d*)$/.test(b)) {

And maintains all existing mathematical constraints (gcd(a,26)=1)

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