feat: add 6 more skins (PS1, PS3, Wii, NDS, Dreamcast, JV2002)

Brings the catalog to nine. Each is a single scoped [data-theme="..."]
CSS file plus a registry entry — no markup changes.

- ps1: charcoal BIOS, gray panels, uppercase letterspacing
- ps3: animated XMB sky gradient + drifting wave, black glass
- wii: white channels, rounded pills, soft blue glow
- nds: silver shell with content framed as the touch screen
- dreamcast: cream BIOS, conic-gradient orange swirl, lowercase blue
- jv2002: dense boxy portal, Verdana 11px, red masthead, blue nav tabs

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

src/app/admin/login/page.tsx

@@ -0,0 +1,38 @@
+import { loginAction } from "../actions";
+
+export default async function LoginPage({
+  searchParams,
+}: {
+  searchParams: Promise<{ error?: string; next?: string }>;
+}) {
+  const { error, next } = await searchParams;
+
+  return (
+    <div className="rb-admin-login">
+      <form className="rb-admin-card rb-login-card" action={loginAction}>
+        <h1 className="rb-admin-h1">RetroBlog Admin</h1>
+        <p className="rb-admin-muted">Sign in to manage posts and settings.</p>
+
+        {error && (
+          <p className="rb-admin-error">Incorrect password. Try again.</p>
+        )}
+
+        <label className="rb-field">
+          <span>Password</span>
+          <input
+            type="password"
+            name="password"
+            autoFocus
+            autoComplete="current-password"
+          />
+        </label>
+
+        {next && <input type="hidden" name="next" value={next} />}
+
+        <button className="rb-btn rb-btn-primary" type="submit">
+          Sign in
+        </button>
+      </form>
+    </div>
+  );
+}