fix(commons): import kotlinx.coroutines.IO so the iOS targets build

`Dispatchers.IO` is an internal member in common code; the public form on
Kotlin/Native is the `kotlinx.coroutines.IO` extension property. Without that
import the member resolves on JVM and Android and fails only on iOS, which is
precisely what commons' compile-only iOS spike exists to surface.

MergedTopFeedAuthorListsState moved into commonMain in 3f4723437e and was the one
file that came across without the import — the other 22 commonMain users of
Dispatchers.IO already have it, and the only other three files that mention it do
so in comments. One error, one file, one missing import.

Reproduced locally with :commons:compileKotlinIosSimulatorArm64 before fixing;
both iOS targets, JVM, Android and the full test suite pass after.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/topNavFeeds/MergedTopFeedAuthorListsState.kt

@@ -33,6 +33,7 @@ import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
 import com.vitorpamplona.quartz.utils.mapOfSet
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.IO
 import kotlinx.coroutines.flow.SharingStarted
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.combine
@@ -100,6 +101,9 @@ class MergedTopFeedAuthorListsState(
                     notificationNavFilter.value,
                 ),
             )
+            // `kotlinx.coroutines.IO` must stay imported: `Dispatchers.IO` is an internal member in
+            // common, and the public form on Kotlin/Native is that extension. Drop the import and this
+            // still builds on JVM/Android, failing only the iOS targets.
         }.flowOn(Dispatchers.IO)
             .stateIn(
                 scope,