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 {