Fix: back button on finder screen exits app instead of closing finder

The hot/cold FinderScreen is a full-screen overlay with no BackHandler, so system-back fell through to the Activity and finished it. Added BackHandler(onBack = onClose) so back closes the finder and returns to the main list. Release 0.1.3.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0187UiEtasyowhEBYs6s9iF5

app/build.gradle.kts

@@ -13,8 +13,8 @@ android {
         applicationId = "org.soulstone.vigil"
         minSdk = 26
         targetSdk = 35
-        versionCode = 3
-        versionName = "0.1.2"
+        versionCode = 4
+        versionName = "0.1.3"
     }
 
     // Fixed debug keystore committed to the repo (a debug key is non-secret — its

app/src/main/kotlin/org/soulstone/vigil/ui/MainScreen.kt

@@ -1,6 +1,7 @@
 package org.soulstone.vigil.ui
 
 import android.text.format.DateUtils
+import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.material.icons.filled.NotificationsActive
 import androidx.compose.material.icons.filled.Sensors
@@ -432,6 +433,8 @@ private fun DetailRow(label: String, value: String) {
  *  proximity meter. Works even on silent/modified tags that refuse to ring. */
 @Composable
 private fun FinderScreen(t: TrackerEntity, onRing: (TrackerEntity) -> Unit, onClose: () -> Unit) {
+    // Intercept system back so it closes the finder instead of exiting the app.
+    BackHandler(onBack = onClose)
     val rssi by ScanService.finderRssi.collectAsState()
     val smoothed = remember { mutableStateOf(-100f) }
     LaunchedEffect(rssi) { rssi?.let { smoothed.value = 0.35f * it + 0.65f * smoothed.value } }