fix(visualizer): auto-enable actually starts capture; persist audio device

Auto-enable was a no-op
- Writing 'visualizerEnabled'='true' to localStorage from app.js did
  not update the exported `let visualizerEnabled` in player.js. So
  applyVisualizerMode() saw the stale `false` and went into the
  DISABLE branch — leaving the device 'available, not capturing'.
- Add a setVisualizerEnabled() setter exported from player.js and
  call it before applyVisualizerMode() during boot.

Audio device persistence
- Save the selected device name to localStorage on change.
- On loadAudioDevices(), prefer status.current_device (server's
  current state) but fall back to the localStorage value if the
  server doesn't know one (e.g. after a server restart).
- If the saved device wasn't recognized by the server, push it back
  via POST /api/media/visualizer/device so capture lands on it
  immediately. Best-effort; no toast on failure.

media_server/static/js/app.js

@@ -22,7 +22,7 @@ import {
     initTheme, toggleTheme, initAccentColor, applyAccentColor,
     renderAccentSwatches, selectAccentColor, toggleAccentPicker, lightenColor,
     toggleVinylMode, applyVinylMode,
-    visualizerEnabled, visualizerAvailable,
+    visualizerEnabled, visualizerAvailable, setVisualizerEnabled,
     checkVisualizerAvailability, toggleVisualizer, applyVisualizerMode,
     loadAudioDevices, onAudioDeviceChanged,
     setupProgressDrag, updateUI, updatePlaybackState, stopPositionInterpolation,
@@ -186,14 +186,13 @@ window.addEventListener('DOMContentLoaded', async () => {
     // Initialize audio visualizer — auto-enable when supported so the
     // spectrum shows real audio out of the box.
     checkVisualizerAvailability().then(() => {
-        if (visualizerAvailable && !visualizerEnabled) {
-            // Auto-enable on first install if loopback capture works.
-            if (localStorage.getItem('visualizerEnabled') === null) {
-                localStorage.setItem('visualizerEnabled', 'true');
-            }
-        }
-        if ((visualizerEnabled || localStorage.getItem('visualizerEnabled') === 'true')
-            && visualizerAvailable) {
+        if (!visualizerAvailable) return;
+        // First install: opt the user in by default since the spectrum
+        // is the centerpiece of the player view.
+        const stored = localStorage.getItem('visualizerEnabled');
+        const shouldEnable = stored === null ? true : stored === 'true';
+        if (shouldEnable) {
+            setVisualizerEnabled(true);   // updates the let in player.js
             applyVisualizerMode();
         }
     });

media_server/static/js/player.js

@@ -277,6 +277,10 @@ function updateVinylSpin() {
 // Audio Visualizer
 export let visualizerEnabled = localStorage.getItem('visualizerEnabled') === 'true';
 export let visualizerAvailable = false;
+export function setVisualizerEnabled(value) {
+    visualizerEnabled = !!value;
+    localStorage.setItem('visualizerEnabled', visualizerEnabled);
+}
 let visualizerCtx = null;
 let visualizerAnimFrame = null;
 export let frequencyData = null;
@@ -506,13 +510,24 @@ export async function loadAudioDevices() {
             select.appendChild(opt);
         }
 
-        if (status.current_device) {
+        // Prefer server-reported device; fall back to the last user choice
+        // saved in localStorage (so reloads persist even if the server
+        // forgets between restarts).
+        const savedDevice = localStorage.getItem('audioDevice') || '';
+        const targetDevice = status.current_device || savedDevice;
+        let pendingPushToServer = false;
+        if (targetDevice) {
             for (let i = 0; i < select.options.length; i++) {
-                if (select.options[i].value === status.current_device) {
+                if (select.options[i].value === targetDevice) {
                     select.selectedIndex = i;
                     break;
                 }
             }
+            // If the saved device wasn't on the server, push it back so
+            // capture starts on the right one.
+            if (!status.current_device && savedDevice) {
+                pendingPushToServer = true;
+            }
         }
 
         // Enhance with icon grid
@@ -545,6 +560,19 @@ export async function loadAudioDevices() {
                 ws.send(JSON.stringify({ type: 'enable_visualizer' }));
             }
         }
+
+        // If the user's previously-chosen device wasn't recognized by
+        // the server (e.g. server restart cleared in-memory state),
+        // push it back so capture lands on the right one.
+        if (pendingPushToServer && savedDevice) {
+            try {
+                await fetch('/api/media/visualizer/device', {
+                    method: 'POST',
+                    headers: { 'Content-Type': 'application/json', ...getAuthHeaders() },
+                    body: JSON.stringify({ device_name: savedDevice })
+                });
+            } catch (_) { /* best-effort */ }
+        }
     } catch (e) {
         section.style.display = 'none';
     }
@@ -572,6 +600,13 @@ export async function onAudioDeviceChanged() {
 
     const deviceName = select.value || null;
 
+    // Persist locally so reloads survive even if the server doesn't.
+    if (deviceName) {
+        localStorage.setItem('audioDevice', deviceName);
+    } else {
+        localStorage.removeItem('audioDevice');
+    }
+
     try {
         const resp = await fetch('/api/media/visualizer/device', {
             method: 'POST',