feat(memory): add Sync lifecycle method and graceful shutdown sync

MemoryStore.Sync() delegates to underlying replica syncer if available.
Agent loop now syncs memory before closing on shutdown, preventing data
loss for Turso embedded replicas.

pkg/agent/loop.go

@@ -274,6 +274,10 @@ func (al *AgentLoop) Run(ctx context.Context) error {
 func (al *AgentLoop) Stop() {
 	al.running.Store(false)
 	if al.memoryStore != nil {
+		if err := al.memoryStore.Sync(); err != nil {
+			logger.WarnCF("agent", "Failed to sync memory before shutdown",
+				map[string]interface{}{"error": err.Error()})
+		}
 		al.memoryStore.Close()
 	}
 }

pkg/memory/store/memory_store.go

@@ -500,6 +500,16 @@ func (m *MemoryStore) OffloadToolResult(ctx context.Context, toolName, content,
 
 // --- Lifecycle ---
 
+// Sync flushes pending writes to the remote replica (Turso).
+// No-op if the underlying delegate doesn't support replication.
+func (m *MemoryStore) Sync() error {
+	type syncer interface{ Sync() error }
+	if s, ok := m.delegate.(syncer); ok {
+		return s.Sync()
+	}
+	return nil
+}
+
 func (m *MemoryStore) Close() error {
 	return m.delegate.Close()
 }