Add documentation field to all crate Cargo.toml files

[randlee]

The documentation field is not set in any crate's Cargo.toml, so docs.rs doesn't get linked on the crates.io pages.

Fix: Add to [workspace.package] in root Cargo.toml:

documentation = "https://docs.rs/wyvern-cli"

Or set per-crate for each crate that should link to its own docs.rs page:

documentation = "https://docs.rs/wyvern-schema"   # in wyvern-schema
documentation = "https://docs.rs/wyvern-host"     # in wyvern-host

The workspace package approach is simpler if all crates share one docs entry point.