fix: camera button (📷) intercepted by kiosk native btnSettings overlay

- Kiosk (Android): btnSettings was positioned top|end with alpha=0.12,
  sitting invisibly on top of the HTML scan button in the webapp header.
  Moved to bottom|end (marginBottom=80dp, alpha=0.28) so it never
  overlaps the header. Kiosk versionCode 15→16, versionName 1.7.15.
- Web (Android Chrome/Brave): pointerleave fired before pointerup when
  finger drifted, cancelling the long-press timer and letting a synthetic
  click bubble to an unintended handler. Fixed with setPointerCapture +
  preventDefault + replaced pointerleave with pointercancel. Added
  touch-action:manipulation to .header-scan-btn CSS.

evershelf-kiosk/app/build.gradle.kts

@@ -11,8 +11,8 @@ android {
         applicationId = "it.dadaloop.evershelf.kiosk"
         minSdk = 24
         targetSdk = 34
-        versionCode = 15
-        versionName = "1.7.14"
+        versionCode = 16
+        versionName = "1.7.15"
     }
 
     signingConfigs {

evershelf-kiosk/app/src/main/res/layout/activity_kiosk.xml

@@ -43,17 +43,18 @@
         android:layout_height="match_parent"
         android:visibility="gone" />
 
-    <!-- Settings gear (shown after setup, over WebView) — top-right corner to avoid overlapping modals -->
+    <!-- Settings gear (shown after setup, over WebView) — bottom-right corner so it never
+         overlaps the webapp header buttons (e.g. the 📷 scan button at top-right) -->
     <ImageButton
         android:id="@+id/btnSettings"
         android:layout_width="44dp"
         android:layout_height="44dp"
-        android:layout_gravity="top|end"
-        android:layout_marginTop="8dp"
+        android:layout_gravity="bottom|end"
+        android:layout_marginBottom="80dp"
         android:layout_marginEnd="8dp"
         android:background="@android:color/transparent"
         android:src="@android:drawable/ic_menu_manage"
-        android:alpha="0.12"
+        android:alpha="0.28"
         android:contentDescription="Settings"
         android:scaleType="centerInside"
         android:visibility="gone" />