add loading to start/stop fab

sensorhub-android-app/res/drawable/ic_loading.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:pathData="M12,4V2C6.48,2 2,6.48 2,12h2c0,-4.42 3.58,-8 8,-8z"
+        android:fillColor="@android:color/white" />
+</vector>

sensorhub-android-app/res/drawable/ic_loading_animated.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<animated-rotate xmlns:android="http://schemas.android.com/apk/res/android"
+    android:drawable="@drawable/ic_loading"
+    android:pivotX="50%"
+    android:pivotY="50%" />

sensorhub-android-app/src/org/sensorhub/android/DashboardFragment.java

@@ -169,17 +169,36 @@ private void updateFabIcon() {
         }
     }
 
+    private void showFabProgress() {
+        if (fab == null) return;
+        fab.setImageResource(R.drawable.ic_loading_animated);
+        fab.setEnabled(false);
+    }
+
+    private void hideFabProgress() {
+        if (fab == null) return;
+        fab.setEnabled(true);
+        updateFabIcon();
+    }
+
     private void stopHub() {
-        Toast.makeText(requireContext(), R.string.stopping_sensorhub, Toast.LENGTH_SHORT).show();
+        showFabProgress();
+        newStatusMessage(getString(R.string.stopping_sensorhub));
         stopRefreshingStatus();
-        provider.stopSensorHub();
-        updateFabIcon();
         hideVideoPreview();
         clearTextureView();
         videoStatusCard.setVisibility(View.GONE);
         if (meshtasticCard != null) meshtasticCard.setVisibility(View.GONE);
-        newStatusMessage(getString(R.string.sensorhub_stopped));
-        requireActivity().getWindow().clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
+        provider.stopSensorHub();
+
+        // Brief delay to let the service finish stopping on its background thread
+        displayHandler.postDelayed(() -> {
+            if (!isAdded()) return;
+            hideFabProgress();
+            updateFabIcon();
+            newStatusMessage(getString(R.string.sensorhub_stopped));
+            requireActivity().getWindow().clearFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
+        }, 1000);
     }
 
     private void clearTextureView() {
@@ -231,7 +250,7 @@ public void onClick(DialogInterface dialog, int whichButton) {
                     showVideoConfigErrorPopup();
                     newStatusMessage(getString(R.string.video_config_error));
                 } else {
-                    Toast.makeText(requireContext(), R.string.starting_sensorhub, Toast.LENGTH_SHORT).show();
+                    showFabProgress();
                     newStatusMessage(getString(R.string.starting_sensorhub));
                     provider.getSostClients().clear();
                     provider.getConSysClients().clear();
@@ -280,6 +299,7 @@ private void pollHubReady() {
 
             if (!provider.isOshStarted()) {
                 provider.setOshStarted(true);
+                hideFabProgress();
                 updateFabIcon();
                 serverStatusContainer.removeAllViews();
                 serverCardViews.clear();
@@ -292,6 +312,7 @@ private void pollHubReady() {
         } else if (hubPollAttempts < HUB_POLL_MAX_ATTEMPTS) {
             displayHandler.postDelayed(this::pollHubReady, HUB_POLL_INTERVAL_MS);
         } else {
+            hideFabProgress();
             newStatusMessage(getString(R.string.sensorhub_start_failed));
             updateFabIcon();
         }