feat(docs): version-bound release documentation served at /docs

Adds a docs pipeline so each release has a version-bound Markdown
document (docs/releases/vX.Y.Z.md) rendered publicly in the app:

- sync-release-docs.mjs copies docs/releases/*.md into the toolrate
  public dir and generates index.json before every dev/build
- /docs lists all releases; /docs/:version renders the sanitized
  Markdown (marked + DOMPurify, typography styles)
- template + workflow documented in docs/README.md
- current release (v0.6.0) documented as the first entry

artifacts/toolrate/src/components/breadcrumbs.tsx

@@ -37,6 +37,10 @@ function buildCrumbs(location: string, t: TFunction): Crumb[] {
     crumbs.push({ label: t("compare.title") });
   } else if (location.startsWith("/analytics")) {
     crumbs.push({ label: t("nav.analytics") });
+  } else if (location.startsWith("/docs")) {
+    crumbs.push({ href: "/docs", label: t("nav.docs") });
+    const match = location.match(/^\/docs\/(.+)$/);
+    if (match) crumbs.push({ label: match[1] });
   } else if (location.startsWith("/login")) {
     crumbs.push({ label: t("auth.signIn") });
   }