Implement remaining code review suggestions

- Add graceful shutdown with SIGTERM/SIGINT handling\n- Make model list configurable via config.yaml\n- Remove sensitive data from debug logs (log sizes instead of full bodies)\n- Handle array format in system messages (both string and []interface{})\n- Update config.yaml with new models structure

converter.go

@@ -53,8 +53,18 @@ func extractSystemMessage(messages []Message) (string, []Message) {
 
 	for _, msg := range messages {
 		if msg.Role == "system" {
-			if content, ok := msg.Content.(string); ok {
+			switch content := msg.Content.(type) {
+			case string:
 				systemParts = append(systemParts, content)
+			case []interface{}:
+				// Extract text from content array
+				for _, part := range content {
+					if partMap, ok := part.(map[string]interface{}); ok {
+						if text, ok := partMap["text"].(string); ok {
+							systemParts = append(systemParts, text)
+						}
+					}
+				}
 			}
 		} else {
 			rest = append(rest, msg)