Add client volume settings and harden screenshot publishing

- persist client config from MQTT for display manager volume control
- apply effective VLC volume from event volume and client multiplier
- support live runtime volume updates for active video playback
- make latest screenshot handoff atomic to avoid broken latest.jpg races
- ignore broken screenshot pointers when selecting fallback images
- fix screenshot size logging and document server-side volume control

src/simclient.py

@@ -143,6 +143,7 @@ logging.info(f"Monitoring logger initialized: {MONITORING_LOG_PATH}")
 
 # Health state file (written by display_manager, read by simclient)
 HEALTH_STATE_FILE = os.path.join(os.path.dirname(__file__), "current_process_health.json")
+CLIENT_SETTINGS_FILE = os.path.join(os.path.dirname(__file__), "config", "client_settings.json")
 
 
 discovered = False
@@ -509,8 +510,13 @@ def get_latest_screenshot():
                 logging.debug(f"Could not read latest.jpg, falling back to newest file: {e}")
             
         # Find the most recent screenshot file
-        screenshot_files = [f for f in os.listdir(screenshot_dir) 
-                          if f.lower().endswith(('.png', '.jpg', '.jpeg'))]
+        # Exclude 'latest.jpg' (it's just a pointer) and any broken symlinks
+        screenshot_files = [
+            f for f in os.listdir(screenshot_dir)
+            if f.lower().endswith(('.png', '.jpg', '.jpeg'))
+            and f != 'latest.jpg'
+            and os.path.exists(os.path.join(screenshot_dir, f))
+        ]
         
         if not screenshot_files:
             return None
@@ -554,6 +560,27 @@ def read_health_state():
         return None
 
 
+def save_client_settings(settings_data):
+    """Persist dashboard-managed client settings for the display manager."""
+    try:
+        os.makedirs(os.path.dirname(CLIENT_SETTINGS_FILE), exist_ok=True)
+        with open(CLIENT_SETTINGS_FILE, 'w', encoding='utf-8') as f:
+            json.dump(settings_data, f, ensure_ascii=False, indent=2)
+        logging.info(f"Client settings saved to {CLIENT_SETTINGS_FILE}")
+    except Exception as e:
+        logging.error(f"Error saving client settings: {e}")
+
+
+def delete_client_settings():
+    """Delete persisted client settings so defaults apply again."""
+    try:
+        if os.path.exists(CLIENT_SETTINGS_FILE):
+            os.remove(CLIENT_SETTINGS_FILE)
+            logging.info(f"Client settings deleted: {CLIENT_SETTINGS_FILE}")
+    except Exception as e:
+        logging.error(f"Error deleting client settings: {e}")
+
+
 def publish_health_message(client, client_id):
     """Publish health status to server via MQTT"""
     try:
@@ -883,6 +910,28 @@ def main():
     client.message_callback_add(group_id_topic, on_group_id_message)
     logging.info(f"Current group_id at start: {current_group_id if current_group_id else 'none'}")
 
+    config_topic = f"infoscreen/{client_id}/config"
+    def on_config_message(client, userdata, msg, properties=None):
+        payload = msg.payload.decode().strip()
+        if not payload or payload.lower() in ("null", "none", "empty", "{}"):
+            logging.info("Empty client config received - deleting persisted client settings")
+            delete_client_settings()
+            return
+
+        try:
+            config_data = json.loads(payload)
+        except json.JSONDecodeError as e:
+            logging.error(f"Invalid JSON in client config message: {e}")
+            return
+
+        if not isinstance(config_data, dict):
+            logging.warning("Ignoring non-object client config payload")
+            return
+
+        save_client_settings(config_data)
+
+    client.message_callback_add(config_topic, on_config_message)
+
     # Discovery-Phase: Sende Discovery bis ACK empfangen
     # The loop is already started, just wait and send discovery messages
     discovery_attempts = 0