Bring the documentation and the website up to the unreleased changes

[zoosky]

Documentation only: no code, no manifests, no behaviour. Five things the pages did not say since 0.10.0, found by auditing every page against the Unreleased changelog.

What changed

• A Command line page on the site (/docs/cli), third in the navigation after Rust and JavaScript. The three pages after it are renumbered (04.language, 05.architecture, 06.divergences) so the order reads that way; slugs come from the name, so no link changes. The docs index gains a "Start here" row and no longer routes "a CLI" to the Rust page.
• A Command line section in the root README, with install, the three commands a CI pipeline uses, and a pointer to the crate README. The MSRV line now says 1.96, which is what the CI job runs; it said 1.82.
• The landing page's "The same engine in a browser" feature is "…in a browser, and in a shell".
• The JavaScript page and the npm README record what Share the schema vocabulary between the hosts #48 changed: the vocabulary is shared with the command line (one schema file serves both hosts, linked); a schema object is read key by key, so a class instance or proxy works; an undefined variable is null; a type list may not nest; a property whose getter throws is refused as unreadable rather than read as absent. The npm README ships with the next release.
• The architecture page's lead and description said "one trait seam, two responsibilities left outside" above a body that said three traits; both now match. Its workspace table lists all three members, and the paragraph after it says why a binary is a host and the vocabulary crate is not.

Verified

scripts/build-site.sh builds with the new page; /docs/rust, /docs/javascript, /docs/cli, /docs/language, /docs/architecture and /docs/divergences all come out at their slugs; every /docs/* link across the built site resolves; cargo run --example readme still runs; fmt and the library tests pass.

Review fixes

Eight findings from /code-review and three it cut for room, all taken:

• The overstated claim, in five places: the browser reads an object, not a file. Every page now says the vocabulary is shared, a schema declared for one host is accepted by the other, and a JSON file is the one spelling both read as it stands (JSON.parse in the browser).
• The Command line page: exit 2 for a document fmt cannot settle, and the four-pass bound stated; parse's two additions over upstream (bindings-shape positions, a file label) restored; the --var x= → null row; the vocabulary crate named and linked.
• Navigation and metadata: the theme's hand-written footer gains the page; site/config.yaml's llms description and the landing page's description name the command line.
• CHANGELOG: the command-line host "will" read through the vocabulary crate → it does.
• tests/readme.rs pins the README's MSRV sentence to CARGO_PKG_RUST_VERSION, so the drift that put 1.82 on the front page cannot recur silently.
• The crate README leads with cargo install --path, as the outer pages do.

Rebuilt the site: the footer on every page links /docs/cli, llms.txt names the command line, all six doc slugs present.