docs: add state-management strategy reference and SQLDelight session log

Added documentation outlining the recommended frontend state-management approach using Unidirectional Data Flow (UDF). Documented the 2026-01-28 session addressing the critical SQLDelight async issue, detailing the analysis, fix implementation, and results. Updated PingEventRepositoryImpl to use `awaitAsOneOrNull` for proper async handling.

frontend/features/ping-feature/src/commonMain/kotlin/at/mocode/ping/feature/data/PingEventRepositoryImpl.kt

@@ -3,6 +3,7 @@ package at.mocode.ping.feature.data
 import at.mocode.frontend.core.localdb.AppDatabase
 import at.mocode.frontend.core.sync.SyncableRepository
 import at.mocode.ping.api.PingEvent
+import app.cash.sqldelight.async.coroutines.awaitAsOneOrNull
 
 // ARCH-BLUEPRINT: This repository implements the generic SyncableRepository
 // for a specific entity, bridging the gap between the sync core and the local database.
@@ -12,12 +13,9 @@ class PingEventRepositoryImpl(
 
   // The `since` parameter for our sync is the ID of the last event, not a timestamp.
   override suspend fun getLatestSince(): String? {
-      println("PingEventRepositoryImpl: getLatestSince called")
-      // WORKAROUND: executeAsOneOrNull() fails with "driver is asynchronous" error.
-      // This seems to be a bug or configuration issue where the sync version is called.
-      // Since we are in Phase 2 (Tracer Bullet), we can live with a full sync for now.
-      // We return null to force a full sync, which works because upsert() works.
-      return null
+      println("PingEventRepositoryImpl: getLatestSince called - using corrected async implementation")
+      // FIX: Use .awaitAsOneOrNull() for async drivers instead of the blocking .executeAsOneOrNull()
+      return db.appDatabaseQueries.selectLatestPingEventId().awaitAsOneOrNull()
   }
 
   override suspend fun upsert(items: List<PingEvent>) {