docs: rename docs/components to docs/crates

The generated landing page's own H1 already said "Crate reference" —
the directory name should match. Rename docs/components/ -> docs/crates/
and update the generating derivation (nix/packages/reference-docs.nix),
its default.nix caller comment, and docs/README.md's link.

Fixes #3193

docs/crates/README.md

@@ -0,0 +1,13 @@
+# Crate reference
+
+One page per Rust workspace crate — its own `README.md`, unchanged, served
+here for browsing alongside the rest of the docs site. **The crate's own
+`README.md` is the source of truth; nothing here is hand-maintained.**
+Every page is generated at build time (`nix/packages/reference-docs.nix`,
+hyperhive#3051) straight from the crate's real `README.md`, so it can never
+drift out of sync the way a hand-copied mirror would — edit the crate's
+own README to change what shows up here.
+
+For the one-line-per-crate index (which crate does what, at a glance)
+see the main [`CLAUDE.md`](../../CLAUDE.md#repo-map) repo map instead;
+this section is each crate's own, longer word on itself.