Add archive component: ZIP/tar/gzip extract and create

[Copilot]

New Wasm component for archive creation and extraction operating entirely on byte arrays — no filesystem I/O.

WIT interface (wit/world.wit)

record file-entry {
    name: string,
    data: list<u8>,
    permissions: option<u32>,   // Unix mode bits
}

export extract:      func(input: list<u8>)          -> result<list<file-entry>, string>;
export create-zip:   func(files: list<file-entry>)  -> result<list<u8>, string>;
export create-tar-gz: func(files: list<file-entry>) -> result<list<u8>, string>;

Implementation

• extract — auto-detects format from magic bytes: ZIP (PK\x03\x04), gzip (\x1F\x8B), fallback to tar. Gzip payloads that contain a POSIX/GNU tar archive are extracted transparently as tar.gz.
• create-zip — zip crate pinned to >=2.3 to avoid the path-canonicalization CVE present in >=1.3,<2.3. Unix permissions round-trip.
• create-tar-gz — tar + flate2 with the pure-Rust miniz_oxide backend. Permissions preserved; entries without permissions default to 0o644.

Other

• justfile and README.md updated to include archive.