feat: Add loading progress indicator

- ProgressBar in activity_main.xml (top of screen)
- LoadingProgress.kt utility with WebChromeClient
- Shows during page load, hides on complete
- Smooth UX with slight hide delay

Integration: webView.setupProgressBar(binding.progressBar)

app/src/main/res/layout/activity_main.xml

@@ -8,6 +8,19 @@
         android:layout_width="match_parent"
         android:layout_height="match_parent" />
 
+    <!-- Loading progress bar (top of screen) -->
+    <ProgressBar
+        android:id="@+id/progressBar"
+        style="@style/Widget.AppCompat.ProgressBar.Horizontal"
+        android:layout_width="match_parent"
+        android:layout_height="4dp"
+        android:layout_gravity="top"
+        android:indeterminate="false"
+        android:max="100"
+        android:progress="0"
+        android:progressTint="@color/progress_color"
+        android:visibility="gone" />
+
     <!-- Invisible admin tap area (top-left corner) -->
     <View
         android:id="@+id/adminTapArea"