Public tree view: full-width canvas like the member view

The public layout forced max-w-5xl on every /p page, so the tree chart was
cramped. Mirror the member shell: the public layout now drops the max-width for
the tree page (/p/<id>) only, giving the chart the full canvas (74vh to match
the member view), while the page keeps its heading and people list in a
centered max-w-5xl column. Person detail (/p/<id>/persons/<pid>) and /explore
stay narrow.

tsc clean; next build passes.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/app/p/layout.tsx

@@ -1,11 +1,21 @@
+"use client";
+
+import { usePathname } from "next/navigation";
+
 import { PublicHeader } from "@/components/public-header";
 
-// Public viewing surface — no auth, no app sidebar. A slim header only.
+// Public viewing surface — no auth, no app sidebar. The tree page (/p/<id>)
+// wants the whole canvas like the member tree view; the person detail page
+// reads better in a centered column.
 export default function PublicLayout({ children }: { children: React.ReactNode }) {
+  const pathname = usePathname();
+  const fullWidth = /^\/p\/[^/]+$/.test(pathname);
   return (
     <div className="min-h-screen">
       <PublicHeader />
-      <main className="mx-auto max-w-5xl px-4 py-8">{children}</main>
+      <main className={fullWidth ? "w-full px-4 py-6 md:px-6" : "mx-auto max-w-5xl px-4 py-8"}>
+        {children}
+      </main>
     </div>
   );
 }