fix: suppress login screen flash on load when already authenticated

Adds a synchronous inline script that checks localStorage before first
paint and sets html.ns-authed, hiding #setup-screen via CSS immediately.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

styles.css

@@ -18,6 +18,7 @@ html,body{height:100%;font-family:var(--font);background:var(--bg);color:var(--t
 ::-webkit-scrollbar{width:4px}::-webkit-scrollbar-track{background:transparent}::-webkit-scrollbar-thumb{background:var(--surface2);border-radius:2px}
 
 /* ── SETUP ── */
+html.ns-authed #setup-screen{display:none}
 #setup-screen{position:fixed;inset:0;z-index:1000;display:flex;align-items:center;justify-content:center;background:var(--bg);background-image:radial-gradient(ellipse 60% 50% at 30% 50%,rgba(232,160,32,.08) 0%,transparent 70%),radial-gradient(ellipse 40% 60% at 80% 30%,rgba(80,60,160,.1) 0%,transparent 70%)}
 .setup-card{width:min(420px,calc(100vw - 32px));background:var(--surface);border:1px solid var(--border2);border-radius:20px;padding:40px 36px;box-shadow:0 40px 80px rgba(0,0,0,.6),0 0 0 1px rgba(255,255,255,.04)}
 .setup-logo{display:flex;align-items:center;gap:12px;margin-bottom:28px}