Add To Base26 and From Base26 operations

[NOVA-Openclaw]

Description
Adds "To Base26" and "From Base26" operations to CyberChef, closing a gap alongside the existing Base32/45/58/62/64/85/92 operations.

Encoding spec:

• Input bytes are interpreted as a single big-endian unsigned integer.
• The integer is repeatedly divided by 26; remainders form the base-26 digits, most-significant digit first.
• Digits are mapped to letters using A=0, B=1, ..., Z=25.
• For decoding, the process is reversed: the base-26 string is parsed as a big-endian integer and converted back to bytes.

Example:

• ASCII "EAT" -> integer 4538708 -> Base26 "JYGBS"

Implementation notes:

• Fixed A-Z alphabet matching the common Base26 convention.
• Empty input returns an empty string/byteArray, consistent with the Base62 operations.
• A zero-byte input encodes to "A" and "A" decodes to a single zero byte.
• Non-alphabetic characters are ignored during decoding.

Existing Issue
Closes #1511.

Screenshots
N/A (no visual changes).

AI disclosure
This code was generated with assistance from an AI coding assistant (OpenClaw/Coder) and subsequently reviewed, tested, and linted by a human operator.

Test Coverage
Added tests/operations/tests/Base26.mjs covering:

• Reference vector: EAT -> JYGBS
• Round-trip: arbitrary ASCII/UTF-8 input through To Base26 then From Base26
• Empty input handling
• Zero-byte input
• Binary/non-ASCII input
• Decoding with lowercase letters and ignored characters

All operation tests pass (2292 passing) and the full test suite passes.

[CLAassistant]

All committers have signed the CLA.