Combine scan+receipts into one flow, add plausibility check,

photo viewing, and record drill-down

- Overview is now the single front page (list + "+" FAB to scan)
  instead of a separate near-empty Scan tab; export moved from
  Overview into the drawer
- Drop petrol_station/transaction_number from storage, the edit
  form, and CSV/ODS export - not useful for a personal fuel-cost log
  (destructive Room migration, version 1->2 already shipped earlier)
- Add a live plausibility check (total_price vs. price_per_litre *
  litres - discount) shown as a green/red badge on the review screen
- Add a shared Details/Photo review screen (ReceiptReviewScreen),
  with pinch-to-zoom on the photo (new Coil dependency), reused both
  right after a scan and when drilling into an already-saved receipt
  from the list (ReceiptDetailScreen, with Update/Delete)
- Fix receipt photos not surviving an app restart: camera/gallery
  captures now write to internal storage (filesDir) instead of the
  cache dir, which the OS can clear independent of the database; the
  gallery picker was also saving the Photo Picker's own short-lived
  content:// Uri instead of a Uri onto our persisted copy
- App log: add a Copy button and selectable text
- Fix the connection status bar overlapping the system gesture nav
  bar under edge-to-edge
- Settings: prefill an editable example server URL, add a "Test
  connection" button; both it and the connection status bar now
  surface the actual failure reason, not just pass/fail

android/gradle/libs.versions.toml

@@ -26,6 +26,7 @@ kotlinxCoroutines = "1.11.0"
 room = "2.8.5"
 splashscreen = "1.0.1"
 okhttp = "4.12.0"
+coil = "3.0.4"
 
 [libraries]
 androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }
@@ -48,6 +49,7 @@ androidx-core-splashscreen = { group = "androidx.core", name = "core-splashscree
 kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-json", version.ref = "kotlinxSerializationJson" }
 kotlinx-coroutines-android = { group = "org.jetbrains.kotlinx", name = "kotlinx-coroutines-android", version.ref = "kotlinxCoroutines" }
 okhttp = { group = "com.squareup.okhttp3", name = "okhttp", version.ref = "okhttp" }
+coil-compose = { group = "io.coil-kt.coil3", name = "coil-compose", version.ref = "coil" }
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }