fix(career): public CV deep links work on direct load, refresh, and shared links

Phase 4.5 (priority 4). The app is a React Router SPA behind Next static
export, which only generated `/` — so a hard load of any deep path (/cv/{slug},
/login, /career/builder/…) hit Next's client not-found before React Router
could route it. Replace the single app/page.tsx with an optional catch-all
app/[[...slug]] (server page + client shell so generateStaticParams stays
server-only) that matches every path; nginx already serves index.html for
unknown paths (try_files), so React Router now owns routing on direct load.

Also: PublicCvPage shows a friendly 404 empty state and sets the document
title. Verified live — /login and /cv/{slug} both resolve on direct navigation.

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

job-tracker-ui/app/page.tsx

@@ -1,12 +0,0 @@
-"use client";
-
-import dynamic from "next/dynamic";
-
-// The whole app is a client-side React Router SPA whose providers read window/localStorage
-// during their initial render -- ssr:false keeps Next's static prerender from ever executing
-// any of it on the server.
-const ClientApp = dynamic(() => import("../src/ClientApp"), { ssr: false });
-
-export default function Page() {
-  return <ClientApp />;
-}