feat: add SFX volume control and improve audio feedback

- Implemented separate sound effects volume control in settings.
- Updated backend to handle new `sfx_volume` parameter.
- Enhanced UI to include sound effects volume slider in admin panel.
- Integrated sound effects for various user interactions (clicks, navigation, alerts).
- Added a new global sound engine to manage audio synthesis without external files.
- Updated documentation for Docker deployment and Windows packaging.
- Refactored audio context management to ensure sound effects are available post user interaction.

backend/static/admin.js

@@ -222,7 +222,20 @@
       volumeLabel.textContent = volumeRange.value + '%';
       if (volTimer) clearTimeout(volTimer);
       volTimer = setTimeout(function () {
-        post('/api/settings', { volume: Number(volumeRange.value) }, function () { toast('音量已更新'); });
+        post('/api/settings', { volume: Number(volumeRange.value) }, function () { toast('媒体音量已更新'); });
+      }, 300);
+    });
+  }
+
+  var sfxVolumeRange = document.getElementById('sfxVolumeRange');
+  var sfxVolumeLabel = document.getElementById('sfxVolumeLabel');
+  var sfxVolTimer = null;
+  if (sfxVolumeRange && sfxVolumeLabel) {
+    sfxVolumeRange.addEventListener('input', function () {
+      sfxVolumeLabel.textContent = sfxVolumeRange.value + '%';
+      if (sfxVolTimer) clearTimeout(sfxVolTimer);
+      sfxVolTimer = setTimeout(function () {
+        post('/api/settings', { sfx_volume: Number(sfxVolumeRange.value) }, function () { toast('音效音量已更新'); });
       }, 300);
     });
   }