Add solution-landscape page and "Where we fit" section

New /landscape page maps the competitive field by category (with named
examples and the gap each leaves), an AlignCare callout, and the combined
job no incumbent owns. Add a compact, competitor-free "Where we fit"
section to the executive summary linking to it, and a Landscape nav item.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/site-header.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { useState } from "react";
-import { FileText, Home, Menu, X } from "lucide-react";
+import { FileText, Home, Layers, Menu, X } from "lucide-react";
 import Link from "next/link";
 import { usePathname } from "next/navigation";
 
@@ -11,6 +11,7 @@ import { cn } from "~/lib/utils";
 const navLinks = [
   { href: "/", label: "About", icon: Home },
   { href: "/executive-summary", label: "Summary", icon: FileText },
+  { href: "/landscape", label: "Landscape", icon: Layers },
 ];
 
 export function SiteHeader() {