docs(fern): migrate OpenShell docs to Fern (#780)

This PR migrates the OpenShell docs to Fern and carries the follow-up cleanup needed to make the migrated site usable and close to the existing docs experience. It focuses on navigation, content structure, code block behavior, and landing-page polish, while leaving CI workflow work out of this PR.

---------

Signed-off-by: Lawrence Lane <llane@nvidia.com>
Co-authored-by: Piotr Mlocek <pmlocek@nvidia.com>

Author: lbliii

.gitignore

@@ -197,3 +197,4 @@ architecture/plans
 .claude/settings.local.json.claude/worktrees/
 .claude/worktrees/
 rfc.md
+.worktrees

fern/assets/NVIDIA_dark.svg

@@ -0,0 +1,26 @@
+/**
+ * Badge links for GitHub, License, PyPI, etc.
+ * Uses a flex wrapper to display badges horizontally and hides Fern's
+ * external-link icon that otherwise stacks under each badge image.
+ * Requires the `.badge-links` CSS rule from main.css.
+ */
+export type BadgeItem = {
+  href: string;
+  src: string;
+  alt: string;
+};
+
+export function BadgeLinks({ badges = [] }: { badges?: BadgeItem[] }) {
+  if (badges.length === 0) {
+    return null;
+  }
+  return (
+    <div className="badge-links">
+      {badges.map((b) => (
+        <a key={b.href} href={b.href} target="_blank" rel="noreferrer">
+          <img src={b.src} alt={b.alt} />
+        </a>
+      ))}
+    </div>
+  );
+}