Add keepsBluetoothAlive hook to Activity base class

Introduces a virtual method allowing activities to indicate whether they need the BLE stack to remain active. This enables selective teardown of Bluetooth to free heap memory, with the Bluetooth settings screen being able to override this for pairing and scanning functionality.

src/activities/settings/BluetoothSettingsActivity.cpp

@@ -6,7 +6,6 @@
 #include <cstdio>
 
 #include "BleButtonMapActivity.h"
-#include "BleInput.h"
 #include "CrossPointSettings.h"
 #include "MappedInputManager.h"
 #include "components/UITheme.h"
@@ -62,12 +61,9 @@ void BluetoothSettingsActivity::handleMenuConfirm() {
   const Action action = menuRows[menuIndex].action;
   switch (action) {
     case Action::ToggleBt:
+      // Flip the preference only; the main-loop lifecycle check starts/stops the BLE
+      // stack to match (and shows the "BT Connecting..." popup). Single owner.
       SETTINGS.bluetoothEnabled = SETTINGS.bluetoothEnabled ? 0 : 1;
-      if (SETTINGS.bluetoothEnabled) {
-        bleinput::ensureStarted();
-      } else {
-        bleinput::stop();
-      }
       SETTINGS.saveToFile();
       rebuildMenuRows();
       requestUpdate();
@@ -238,14 +234,18 @@ void BluetoothSettingsActivity::render(RenderLock&&) {
         },
         true);
   } else if (view == View::Scan) {
+    // Free2/3 remotes only advertise in the right slider mode — tell the user how.
+    GUI.drawHelpText(renderer, Rect{0, topOffset, pageWidth, 16}, tr(STR_BT_FREE_HINT1));
+    GUI.drawHelpText(renderer, Rect{0, topOffset + 16, pageWidth, 16}, tr(STR_BT_FREE_HINT2));
+    const int scanTop = topOffset + 38;
     const int count = BleHid.deviceCount();
     if (count == 0) {
-      GUI.drawHelpText(renderer, Rect{0, topOffset + metrics.verticalSpacing, pageWidth, 24},
+      GUI.drawHelpText(renderer, Rect{0, scanTop, pageWidth, 24},
                        BleHid.isScanning() ? tr(STR_SCANNING) : tr(STR_BT_NO_DEVICES));
     } else {
       GUI.drawList(
-          renderer, listRect, count, scanIndex, [this](int i) { return deviceLabel(i); }, nullptr, nullptr, nullptr,
-          false);
+          renderer, Rect{0, scanTop, pageWidth, contentHeight - 38}, count, scanIndex,
+          [this](int i) { return deviceLabel(i); }, nullptr, nullptr, nullptr, false);
     }
   } else {  // Paired
     const int count = BleHid.pairedCount();