fix: sanitize fcm data payload keys for android

- avoid reserved FCM key names like message_type

- send push metadata in camelCase keys already supported by Android

app/notifications/tasks.py

@@ -81,10 +81,26 @@ def _send_fcm_to_user(user_id: int, title: str, body: str, data: dict[str, Any])
         return
 
     string_data = {
-        **{str(key): str(value) for key, value in data.items()},
         "title": title,
         "body": body,
     }
+    for key, value in data.items():
+        normalized_key = str(key)
+        if normalized_key == "chat_id":
+            normalized_key = "chatId"
+        elif normalized_key == "message_id":
+            normalized_key = "messageId"
+        elif normalized_key == "sender_id":
+            normalized_key = "senderId"
+        elif normalized_key == "message_type":
+            normalized_key = "messageType"
+        elif normalized_key == "preview_image_url":
+            normalized_key = "previewImageUrl"
+        elif normalized_key == "sender_name":
+            normalized_key = "senderName"
+        elif normalized_key == "text_preview":
+            normalized_key = "textPreview"
+        string_data[normalized_key] = str(value)
     for platform, token in tokens:
         webpush = None
         notification = None