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/kotlin/farm/hobbs/kioskbrowser/LoadingProgress.kt

@@ -0,0 +1,46 @@
+package farm.hobbs.kioskbrowser
+
+import android.view.View
+import android.webkit.WebChromeClient
+import android.webkit.WebView
+import android.widget.ProgressBar
+
+/**
+ * WebChromeClient that updates a ProgressBar during page loads.
+ * 
+ * Usage:
+ * ```
+ * webView.webChromeClient = LoadingProgress.createClient(progressBar)
+ * ```
+ */
+object LoadingProgress {
+
+    /**
+     * Create a WebChromeClient that controls the progress bar
+     */
+    fun createClient(progressBar: ProgressBar): WebChromeClient {
+        return object : WebChromeClient() {
+            override fun onProgressChanged(view: WebView?, newProgress: Int) {
+                super.onProgressChanged(view, newProgress)
+                
+                progressBar.progress = newProgress
+                
+                if (newProgress < 100) {
+                    progressBar.visibility = View.VISIBLE
+                } else {
+                    // Hide with slight delay for smooth UX
+                    progressBar.postDelayed({
+                        progressBar.visibility = View.GONE
+                    }, 200)
+                }
+            }
+        }
+    }
+
+    /**
+     * Extension to easily wire up progress tracking
+     */
+    fun WebView.setupProgressBar(progressBar: ProgressBar) {
+        webChromeClient = createClient(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"

app/src/main/res/values/colors.xml

@@ -4,4 +4,5 @@
     <color name="primary_container">#BBDEFB</color>
     <color name="white">#FFFFFF</color>
     <color name="black">#000000</color>
+    <color name="progress_color">#667eea</color>
 </resources>