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/gradle/libs.versions.toml

@@ -8,15 +8,25 @@ compose-multiplatform = "1.11.1"
 # material3 ships on its own release train, separate from the CMP version.
 compose-material3 = "1.9.0"
 androidx-activityCompose = "1.13.0"
+# Declared rather than inherited because this
+# code now calls its extensions directly (SharedPreferences.edit, String
+# .toUri), and a transitive it merely inherited could change under it.
+androidx-core-ktx = "1.19.0"
 zxing-embedded = "4.3.0"
+# Backports java.time (and more) to API 24, which UsageScreen needs: its
+# reset countdown is OffsetDateTime/Duration, both API 26. Checked
+# 2026-08-28 against Google Maven.
+desugar-jdk-libs = "2.1.5"
 
 [libraries]
 androidx-activity-compose = { module = "androidx.activity:activity-compose", version.ref = "androidx-activityCompose" }
+androidx-core-ktx = { module = "androidx.core:core-ktx", version.ref = "androidx-core-ktx" }
 # In-app QR scanner: a ready-made scanning Activity (camera preview, runtime
 # permission prompt, flashlight toggle) reached through the AndroidX Activity
 # Result API (ScanContract, added in 4.3.0). Fully offline -- no Play
 # Services / ML Kit model download involved.
 zxing-embedded = { module = "com.journeyapps:zxing-android-embedded", version.ref = "zxing-embedded" }
+desugar-jdk-libs = { module = "com.android.tools:desugar_jdk_libs", version.ref = "desugar-jdk-libs" }
 # Declared directly rather than through the plugin's `compose.*` accessors,
 # which are deprecated as of CMP 1.11.
 compose-runtime = { module = "org.jetbrains.compose.runtime:runtime", version.ref = "compose-multiplatform" }