feat(web): redirect logged-in users from / to /issues via server-side proxy

Use a lightweight cookie (multica_logged_in) + Next.js 16 proxy to
302-redirect authenticated users visiting / straight to /issues.
Unauthenticated visitors (and search engine crawlers) continue to see
the full landing page with zero flash.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/proxy.ts

@@ -0,0 +1,14 @@
+import { NextResponse } from "next/server";
+import type { NextRequest } from "next/server";
+
+export function proxy(request: NextRequest) {
+  const loggedIn = request.cookies.has("multica_logged_in");
+  if (loggedIn) {
+    return NextResponse.redirect(new URL("/issues", request.url));
+  }
+  return NextResponse.next();
+}
+
+export const config = {
+  matcher: ["/"],
+};