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-sqlite/src/jvmMain/kotlin/pw/binom/agentik/storage/sqlite/SqliteMessageStore.kt

@@ -2,7 +2,7 @@ package pw.binom.agentik.storage.sqlite
 
 import kotlinx.serialization.json.Json
 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 pw.binom.agentik.messageLog.decodeBodyPayload
 import pw.binom.agentik.messageLog.encodeBodyPayload
@@ -19,7 +19,7 @@ import kotlin.time.Instant
  * SQLDelight сохраняет snake_case в сгенерированной data class (`Message`),
  * поэтому обращаемся через `conversation_id`, `payload_json`, `created_at`.
  */
-class SqliteMessageStore(private val db: AgentikDatabase) : MessageStore {
+class SqliteMessageStore(private val db: AgentikDatabase) : MutableMessageStore {
 
     private val q get() = db.messageQueries
 

storage-sqlite/src/jvmMain/kotlin/pw/binom/agentik/storage/sqlite/SqliteStores.kt

@@ -4,7 +4,7 @@ import app.cash.sqldelight.db.QueryResult
 import app.cash.sqldelight.db.SqlDriver
 import app.cash.sqldelight.driver.jdbc.sqlite.JdbcSqliteDriver
 import pw.binom.agentik.messageStore.ConversationStore
-import pw.binom.agentik.messageLog.MessageStore
+import pw.binom.agentik.messageLog.MutableMessageStore
 import pw.binom.agentik.messageStore.ReflectionStore
 import pw.binom.agentik.storage.sqlite.SqliteReflectionStore
 import pw.binom.agentik.workingMemory.WorkingMemoryStore
@@ -15,7 +15,7 @@ import pw.binom.agentik.workingMemory.WorkingMemoryStore
 class SqliteStores private constructor(
     val driver: SqlDriver,
     val conversations: ConversationStore,
-    val messages: MessageStore,
+    val messages: MutableMessageStore,
     val workingMemory: WorkingMemoryStore,
     val reflections: ReflectionStore,
 ) : AutoCloseable {