refactor(message-log-api): split MessageStore into read-only and mutable interfaces

- Introduced `MutableMessageStore` for producers with an `append` operation, separate from read-only `MessageStore`.
- Updated all consumers and implementations to use the appropriate interface (`read-only` for observers, `mutable` for producers).
- Improves modularity and ensures compile-time guarantees against unintended write operations in the audit log.

storage-inmemory/src/commonMain/kotlin/pw/binom/agentik/storage/inmemory/InMemoryMessageStore.kt

@@ -7,7 +7,7 @@ import kotlinx.coroutines.sync.Mutex
 import kotlinx.coroutines.sync.withLock
 import pw.binom.agentik.messageLog.MessageEvent
 import pw.binom.agentik.messageLog.MessageRecord
-import pw.binom.agentik.messageLog.MessageStore
+import pw.binom.agentik.messageLog.MutableMessageStore
 import pw.binom.agentik.messageLog.TokenStats
 import kotlin.time.Instant
 
@@ -22,7 +22,7 @@ import kotlin.time.Instant
  * любом KMP-таргете (включая iOS/native, где SQLite через Android driver
  * недоступен).
  */
-class InMemoryMessageStore : MessageStore {
+class InMemoryMessageStore : MutableMessageStore {
 
     private val byConv: MutableMap<String, MutableList<MessageRecord>> = mutableMapOf()
     private val events = MutableSharedFlow<MessageEvent>(extraBufferCapacity = 64)

storage-inmemory/src/commonMain/kotlin/pw/binom/agentik/storage/inmemory/InMemoryStorage.kt

@@ -1,6 +1,6 @@
 package pw.binom.agentik.storage.inmemory
 
-import pw.binom.agentik.messageLog.MessageStore
+import pw.binom.agentik.messageLog.MutableMessageStore
 import pw.binom.agentik.messageStore.ConversationStore
 import pw.binom.agentik.messageStore.ReflectionStore
 import pw.binom.agentik.workingMemory.WorkingMemoryStore
@@ -22,7 +22,7 @@ import kotlin.time.Clock
 object InMemoryStorage {
     data class Bundle(
         val conversationStore: ConversationStore,
-        val messageStore: MessageStore,
+        val messageStore: MutableMessageStore,
         val workingMemoryStore: WorkingMemoryStore,
         val reflectionStore: ReflectionStore,
     )