Ferritin — Rust documentation

Look up Rust documentation. `get` shows an item by path (e.g. `serde::Deserialize`, `std::vec::Vec`, `tokio@1::runtime::Runtime`). `search` with a `crate` finds items within that crate's documentation by name or prose. `search` without a `crate` searches a different, much shallower dataset — crates.io names, descriptions, and declared keywords — to discover which crate to use; it cannot see any crate's actual documentation, so when you already know the crate, always pass it. The part after `@` is a semver requirement, not an exact version — `tokio@1` serves the newest 1.x; use `tokio@=1.40` to pin an exact release. Output is token-efficient Markdown.