refactor(locale): draw per-app language from floret-kit core-locale

Replace the app-local AppLanguage with the shared
de.jeanlucmakiola.floret.locale.AppLanguage. The kit version is identical
except supportedTags() takes the locales_config XML res id as a parameter
(the kit can't reference the app's R), so the call site now passes
R.xml.locales_config. Wire the core-locale module into the app.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/build.gradle.kts

@@ -160,6 +160,7 @@ dependencies {
 
     implementation(libs.kotlinx.datetime)
     implementation("de.jeanlucmakiola.floret:core-time")
+    implementation("de.jeanlucmakiola.floret:core-locale")
     implementation(libs.kotlinx.coroutines.core)
 
     debugImplementation(libs.androidx.ui.tooling)