Run the linter the app build already had, and fix what it found

`./gradlew :androidApp:lintDebug` had apparently never been run. It
reported 11 errors, 8 warnings and 3 hints, and one of the errors was a
crash: UsageScreen formats its reset countdown with java.time --
OffsetDateTime and Duration, both API 26 -- while minSdk is 24 and core
library desugaring was off. On 24 and 25 that is a NoClassDefFoundError,
and the `catch (_: Exception)` around the code does not stop an Error, so
the usage screen would have died rather than degraded.

Core library desugaring is now on, with desugar_jdk_libs 2.1.5. Verified
by looking in the built APK rather than trusting the flag: it now carries
Lj$/time/Duration and Lj$/time/OffsetDateTime, the backported classes the
call sites are rewritten against.

The rest: the two KTX suggestions taken (SharedPreferences.edit's block
form, which cannot forget its apply(), and String.toUri), the three
autoboxing hints taken (mutableIntStateOf/mutableLongStateOf), and
androidx.core:core-ktx declared at 1.19.0 rather than inherited through
activity-compose, since this code now calls its extensions directly.

Two are suppressed with their reasons, both scoped to the one element.
DiscouragedApi on the scanner's screenOrientation, which is not a pin but
the removal of the library's landscape lock. MissingApplicationIcon,
because there is no icon yet and that is a decision to make later, not an
oversight -- an app with no icon is obvious to anyone who opens a
launcher, so the warning tells nobody here anything.

0 errors now. The 4 warnings left are one thing: Compose Multiplatform
1.12.0 is out and this is on 1.11.1. That is an upgrade to decide on, not
a defect, so it is left for its own change.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017xn8nHw1tw1R6PtiY1eEtw

app/androidApp/build.gradle.kts

@@ -106,6 +106,11 @@ android {
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_21
         targetCompatibility = JavaVersion.VERSION_21
+        // minSdk is 24 and UsageScreen formats its countdown with
+        // java.time, which the platform only has from 26. Without this it
+        // is a NoClassDefFoundError on 24 and 25 -- an Error, so the
+        // catch around that code does not stop it.
+        isCoreLibraryDesugaringEnabled = true
     }
 }
 
@@ -121,10 +126,15 @@ androidComponents {
 }
 
 dependencies {
+    // Not a library this code calls: it is what `isCoreLibraryDesugaring
+    // Enabled` above rewrites java.time against, so API 24 and 25 have it.
+    coreLibraryDesugaring(libs.desugar.jdk.libs)
+
     implementation(libs.compose.runtime)
     implementation(libs.compose.foundation)
     implementation(libs.compose.material3)
     implementation(libs.compose.ui)
     implementation(libs.androidx.activity.compose)
+    implementation(libs.androidx.core.ktx)
     implementation(libs.zxing.embedded)
 }