Capture feedback (shutter sound + flash) and Paperless UX; v0.1.1

- Camera: system shutter sound (only when ringer isn't silenced) + brief
  white flash overlay on capture, for clear feedback even on silent.
- Settings: snackbar confirmation when saving.
- Export: explain why the Paperless upload button is disabled when unconfigured.
- Bump versionCode 2 / versionName 0.1.1.

Fixes #1, #2

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/build.gradle.kts

@@ -24,8 +24,8 @@ android {
         applicationId = "eu.geyskens.pdfscan"
         minSdk = 26
         targetSdk = 35
-        versionCode = 1
-        versionName = "0.1.0"
+        versionCode = 2
+        versionName = "0.1.1"
 
         // OpenCV native libs are large; ship only the ABIs real phones use.
         ndk {