feat: portal selector home page + remove self-serve signup

Replace the home page with a portal selector showing three access paths:
- Organisation Portal → /org/login
- Chapter Portal → /login
- Member Portal → /member-login

Remove /signup and its BFF route — tenants are now only created by org
owners through the org portal or assigned by super admins. Self-serve
community creation is no longer supported.

Update sidebar to bypass auth guard for / (exact match) without
accidentally matching all paths via startsWith.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/web/app/page.tsx

@@ -1,25 +1,63 @@
 import Link from 'next/link';
 
+const PORTALS = [
+  {
+    href: '/org/login',
+    title: 'Organisation Portal',
+    description: 'For org-level admins managing multiple chapters and org-wide rules.',
+    badge: 'Org Admin',
+    color: 'hover:border-violet-400',
+    badgeColor: 'bg-violet-100 text-violet-700',
+  },
+  {
+    href: '/login',
+    title: 'Chapter Portal',
+    description: 'For chapter admins approving messages, managing groups and routing rules.',
+    badge: 'Chapter Admin',
+    color: 'hover:border-blue-400',
+    badgeColor: 'bg-blue-100 text-blue-700',
+  },
+  {
+    href: '/member-login',
+    title: 'Member Portal',
+    description: 'For community members to view digests, manage privacy and explore the directory.',
+    badge: 'Member',
+    color: 'hover:border-emerald-400',
+    badgeColor: 'bg-emerald-100 text-emerald-700',
+  },
+];
+
 export default function Home() {
   return (
-    <div className="flex flex-col gap-6 max-w-xl">
-      <h1 className="text-3xl font-bold tracking-tight">Insignia TOWER</h1>
-      <p className="text-gray-500">Community Knowledge Infrastructure Platform</p>
-      <div className="flex gap-4">
-        <Link
-          href="/search"
-          className="flex-1 rounded-xl border border-gray-200 bg-white p-5 hover:border-blue-400 transition-colors"
-        >
-          <h2 className="font-semibold mb-1">Search</h2>
-          <p className="text-sm text-gray-500">Full-text search of approved messages</p>
-        </Link>
-        <Link
-          href="/groups"
-          className="flex-1 rounded-xl border border-gray-200 bg-white p-5 hover:border-blue-400 transition-colors"
-        >
-          <h2 className="font-semibold mb-1">Groups</h2>
-          <p className="text-sm text-gray-500">Manage groups and sync routes</p>
-        </Link>
+    <div className="min-h-screen flex items-center justify-center bg-gray-50 p-6">
+      <div className="w-full max-w-lg">
+        <div className="mb-10 text-center">
+          <h1 className="text-3xl font-bold tracking-tight text-gray-900">TOWER</h1>
+          <p className="text-gray-500 mt-2 text-sm">Community Knowledge Infrastructure Platform</p>
+        </div>
+
+        <div className="flex flex-col gap-4">
+          {PORTALS.map((p) => (
+            <Link
+              key={p.href}
+              href={p.href}
+              className={`bg-white rounded-2xl border border-gray-200 p-6 flex items-start gap-5 transition-colors ${p.color}`}
+            >
+              <div className="flex-1">
+                <div className="flex items-center gap-2 mb-1">
+                  <h2 className="font-semibold text-gray-900">{p.title}</h2>
+                  <span className={`text-xs font-medium px-2 py-0.5 rounded-full ${p.badgeColor}`}>{p.badge}</span>
+                </div>
+                <p className="text-sm text-gray-500">{p.description}</p>
+              </div>
+              <span className="text-gray-300 text-xl mt-0.5">›</span>
+            </Link>
+          ))}
+        </div>
+
+        <p className="text-center text-xs text-gray-400 mt-8">
+          Administrators are provisioned by your organisation — contact your org admin if you need access.
+        </p>
       </div>
     </div>
   );