feat(player): render announcement banners in soundtouch-player too

The design's three-area target model (chooser/app/admin) and the backend
(HandleListAnnouncements' target=app filtering) already supported this, but
nothing in soundtouch-player's frontend called it — chunk 5 only wired the
admin UI. New Announcements Preact component (static/js/components/), mounted
in App() above the main content so it's visible across every page, styled
with the app's existing CSS variables (dark-mode-aware, unlike the admin
UI's hardcoded inline colors). Currently renders nothing, since no
announcement in the list targets "app" yet (only the admin-gate notice,
targeting "admin") — this is just closing the parity gap so a future
app-targeted announcement has somewhere to show up.

Verified end-to-end against a running instance: the component is served
under /app/static/js/components/, app.js references it, and
/api/announcements?target=app responds correctly (empty today).

Refs #419

pkg/service/soundtouchweb/static/css/app.css

@@ -911,3 +911,34 @@ img { display: block; max-width: 100%; }
     animation: fade-in .2s ease;
 }
 @keyframes fade-in { from { opacity: 0; transform: translateX(-50%) translateY(8px); } }
+
+/* ── Announcements ───────────────────────────────────────────────────────── */
+.announcements-banner {
+    padding: .5rem 1rem 0;
+}
+.announcement {
+    display: flex;
+    align-items: flex-start;
+    justify-content: space-between;
+    gap: .75rem;
+    padding: .6rem .9rem;
+    margin-bottom: .5rem;
+    border-radius: var(--radius);
+    background: var(--surface);
+    border: 1px solid var(--border);
+    color: var(--text);
+    font-size: .85rem;
+}
+.announcement-dismiss {
+    background: none;
+    border: none;
+    cursor: pointer;
+    font-size: 1.1rem;
+    line-height: 1;
+    color: var(--text-dim);
+    flex-shrink: 0;
+    padding: 0;
+}
+.announcement-dismiss:hover {
+    color: var(--text);
+}

pkg/service/soundtouchweb/static/js/app.js

@@ -13,6 +13,7 @@ import { RadioBrowser } from './components/RadioBrowser.js';
 import { Library } from './components/Library.js';
 import { PlayURL } from './components/PlayURL.js';
 import { TTS } from './components/TTS.js';
+import { Announcements } from './components/Announcements.js';
 import { api } from './api.js';
 
 const html = htm.bind(h);
@@ -233,6 +234,8 @@ function App() {
                 </div>
             </nav>
 
+            <${Announcements} />
+
             <main class="main-content">
                 ${page === 'devices' ? html`
                     <${DeviceList}

pkg/service/soundtouchweb/static/js/components/Announcements.js

@@ -0,0 +1,44 @@
+import { h } from 'preact';
+import { useState, useEffect } from 'preact/hooks';
+import htm from 'htm';
+
+const html = htm.bind(h);
+
+// Announcements renders dismissible banners for the player (target=app),
+// mirroring the admin UI's banner (pkg/service/handlers/web/js/script.js,
+// fetchAnnouncements/dismissAnnouncement) against the same backend endpoints
+// added for #419 — see _/i419/design-admin-area-auth-gate.md. Dismissal is
+// recorded server-side (not a client-only localStorage flag), so it stays
+// dismissed across sessions/devices.
+export function Announcements() {
+    const [announcements, setAnnouncements] = useState([]);
+
+    useEffect(() => {
+        fetch('/api/announcements?target=app')
+            .then(res => res.ok ? res.json() : { announcements: [] })
+            .then(data => setAnnouncements(data.announcements || []))
+            .catch(err => console.error('Failed to fetch announcements:', err));
+    }, []);
+
+    async function dismiss(id) {
+        try {
+            await fetch(`/api/announcements/${encodeURIComponent(id)}/dismiss`, { method: 'POST' });
+        } catch (err) {
+            console.error('Failed to dismiss announcement:', err);
+        }
+        setAnnouncements(prev => prev.filter(a => a.id !== id));
+    }
+
+    if (announcements.length === 0) return null;
+
+    return html`
+        <div class="announcements-banner">
+            ${announcements.map(a => html`
+                <div class="announcement announcement-${a.level || 'info'}" key=${a.id}>
+                    <span>${a.message}</span>
+                    <button class="announcement-dismiss" onClick=${() => dismiss(a.id)} title="Dismiss">&times;</button>
+                </div>
+            `)}
+        </div>
+    `;
+}