fix(bluetooth): update filter container ID to btFilterGroup, document sticky offset

static/css/index.css

@@ -4983,6 +4983,7 @@ header h1 .tagline {
     background: var(--bg-primary);
     flex-shrink: 0;
     position: sticky;
+    /* 44px = height of the sticky .wifi-device-list-header above this row */
     top: 44px;
     z-index: 3;
 }

static/js/modes/bluetooth.js

@@ -129,7 +129,7 @@ const BluetoothMode = (function() {
      */
     function initDeviceFilters() {
         if (filterListenersBound) return;
-        const filterContainer = document.getElementById('btDeviceFilters');
+        const filterContainer = document.getElementById('btFilterGroup');
         if (filterContainer) {
             filterContainer.addEventListener('click', (e) => {
                 const btn = e.target.closest('.bt-filter-btn');