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/src/main/kotlin/com/example/aiapp/MainActivity.kt

@@ -16,6 +16,7 @@ import androidx.compose.foundation.layout.statusBarsPadding
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Surface
 import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableIntStateOf
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
@@ -24,7 +25,7 @@ import androidx.core.view.WindowCompat
 class MainActivity : ComponentActivity() {
     // Bumped whenever enrollment lands via an aiapp:// intent so the
     // composition below re-reads the stored settings.
-    private var settingsVersion by mutableStateOf(0)
+    private var settingsVersion by mutableIntStateOf(0)
 
     // Registered up front since permission launchers must be registered
     // before the activity reaches STARTED.