Add an 18+ entry screen before the app renders

A homescreen-style age gate shown before auth or any route: J621 brand
mark, the explicit 18+ check, an Enter action remembered per browser in
localStorage (j621.age-verified), and a blocked state if the visitor
chooses Leave.

ROADMAP.md

@@ -85,6 +85,8 @@ Files now stage first and are resolved before entering the library.
 
 ## 5. Shell & polish
 
+- [x] 18+ entry screen: an age check gates the app before anything renders
+      (remembered per browser in `localStorage`)
 - [ ] Toasts instead of inline messages / confirm dialogs
 - [ ] Mobile drawer polish for metadata panels (design spec §layout)
 - [x] Profile pictures: staff Users page sets avatars from library J-IDs

frontend/src/App.tsx

@@ -1,4 +1,4 @@
-import { useEffect, type ReactNode } from "react";
+import { useEffect, useState, type ReactNode } from "react";
 import {
   Navigate,
   Route,
@@ -10,6 +10,7 @@ import {
 import { AppShell } from "@/components/AppShell";
 import { FullPageSpinner } from "@/components/ui";
 import AccountPage from "@/features/account/AccountPage";
+import { AgeGate } from "@/features/age/AgeGate";
 import LoginPage from "@/features/auth/LoginPage";
 import RegisterPage from "@/features/auth/RegisterPage";
 import DetailPage from "@/features/detail/DetailPage";
@@ -20,6 +21,7 @@ import Md5Redirect from "@/features/library/Md5Redirect";
 import OnlinePage from "@/features/online/OnlinePage";
 import UploadPage from "@/features/upload/UploadPage";
 import UsersPage from "@/features/users/UsersPage";
+import { isAgeVerified, markAgeVerified } from "@/lib/age";
 import { useAuth } from "@/store/auth";
 
 function RequireAuth({ children }: { children: ReactNode }) {
@@ -39,11 +41,23 @@ function PostRedirect() {
 export default function App() {
   const ready = useAuth((state) => state.ready);
   const loadUser = useAuth((state) => state.loadUser);
+  const [ageVerified, setAgeVerified] = useState(isAgeVerified);
 
   useEffect(() => {
     void loadUser();
   }, [loadUser]);
 
+  if (!ageVerified) {
+    return (
+      <AgeGate
+        onEnter={() => {
+          markAgeVerified();
+          setAgeVerified(true);
+        }}
+      />
+    );
+  }
+
   if (!ready) {
     return <FullPageSpinner />;
   }

frontend/src/features/age/AgeGate.tsx

@@ -0,0 +1,75 @@
+import { Ban, ShieldAlert } from "lucide-react";
+import { useState } from "react";
+
+import { Button } from "@/components/ui";
+
+export function AgeGate({ onEnter }: { onEnter: () => void }) {
+  const [declined, setDeclined] = useState(false);
+
+  if (declined) {
+    return (
+      <div className="flex min-h-screen items-center justify-center bg-ctp-crust px-4">
+        <div className="w-full max-w-md rounded-lg border border-ctp-red/40 bg-ctp-base p-6 text-center">
+          <Ban className="mx-auto h-7 w-7 text-ctp-red" />
+          <h1 className="mt-3 text-lg font-semibold text-ctp-text">
+            Access restricted
+          </h1>
+          <p className="mt-2 text-sm leading-relaxed text-ctp-subtext0">
+            You have to be 18 years or older to view this archive. Come back
+            when that applies.
+          </p>
+          <Button
+            variant="secondary"
+            className="mt-5"
+            onClick={() => setDeclined(false)}
+          >
+            Go back
+          </Button>
+        </div>
+      </div>
+    );
+  }
+
+  return (
+    <div className="flex min-h-screen items-center justify-center bg-ctp-crust px-4">
+      <div className="w-full max-w-lg">
+        <div className="flex items-center gap-3">
+          <span className="rounded bg-ctp-mauve px-2.5 py-1.5 font-mono text-sm font-bold tracking-wide text-ctp-crust">
+            J621
+          </span>
+          <span className="font-mono text-[11px] uppercase tracking-widest text-ctp-overlay0">
+            Self-hosted media archive
+          </span>
+        </div>
+
+        <div className="mt-6 rounded-lg border border-ctp-surface0 bg-ctp-base p-6">
+          <div className="flex items-start gap-3">
+            <ShieldAlert className="mt-0.5 h-5 w-5 shrink-0 text-ctp-peach" />
+            <h1 className="text-lg font-semibold leading-snug text-ctp-text">
+              You have to be 18+ to access this site.
+            </h1>
+          </div>
+
+          <p className="mt-3 text-sm leading-relaxed text-ctp-subtext0">
+            This archive contains adult material. By entering you confirm that
+            you are at least 18 years old and that viewing adult content is
+            legal where you live.
+          </p>
+
+          <div className="mt-6 flex flex-col gap-3 sm:flex-row">
+            <Button className="flex-1" autoFocus onClick={onEnter}>
+              I am 18 or older — Enter
+            </Button>
+            <Button variant="secondary" onClick={() => setDeclined(true)}>
+              Leave
+            </Button>
+          </div>
+        </div>
+
+        <p className="mt-4 text-center font-mono text-[11px] text-ctp-overlay0">
+          Local-first library · e621 integration · nothing leaves this server
+        </p>
+      </div>
+    </div>
+  );
+}

frontend/src/lib/age.ts

@@ -0,0 +1,17 @@
+const AGE_KEY = "j621.age-verified";
+
+export function isAgeVerified(): boolean {
+  try {
+    return window.localStorage.getItem(AGE_KEY) === "1";
+  } catch {
+    return false;
+  }
+}
+
+export function markAgeVerified(): void {
+  try {
+    window.localStorage.setItem(AGE_KEY, "1");
+  } catch {
+    // Private mode with storage disabled: the gate simply shows again.
+  }
+}