Add Zstandard (Zstd) Compress and Decompress operations

[lzandman]

Description
Zstandard is a modern lossless compression algorithm developed by Meta. It is widely used in Linux kernels, databases, container images, and network protocols due to its high compression ratio at fast speeds.

This PR contains the following:

• Zstd Compress operation — compresses input data using the Zstandard algorithm, with a configurable compression level (1–22, default: 3).
• Zstd Decompress operation — decompresses Zstd-compressed data, with auto-detection support via the magic bytes 28 B5 2F FD.
• Zstd file type detection in FileSignatures.mjs — recognises both standard Zstd frames and skippable frames (.zst, application/zstd).

Existing Issue
This previously was requested in #1470, though I decided to add this feature based on my own requirements.

Test Coverage

• Compress arbitrary input and verify the output starts with 28 B5 2F FD (Zstd magic bytes).
• Round-trip: compress then decompress, confirm output matches original input.
• Verify auto-detection triggers Zstd Decompress when pasting Zstd-compressed data.
• Confirm compression levels 1 and 22 both produce valid output.
• Run the existing unit tests (tests/operations/tests/Zstd.mjs).

Notes
This PR relies on the @bokuweb/zstd-wasm npm package, which provides a WebAssembly build of the Zstd library.

AI disclosure
Claude Code used to create tests.