MacOS Python3 error export.py unexpected character after line continuation character

[andywirv]

On MacOS with Python 3.11.6

chat.py discover

results in the error :

Traceback (most recent call last):
  File "/Users/andy/projects/cursor-chat-export/chat.py", line 7, in <module>
    from src.export import ChatExporter, MarkdownChatFormatter, MarkdownFileSaver
  File "/Users/andy/projects/cursor-chat-export/src/export.py", line 92
    user_text.append(f"[selections]  \n{"\n".join([s["text"] for s in bubble['selections']])}")
                                          ^
SyntaxError: unexpected character after line continuation character

This PR fixes the issue in the f-string with the use of backslash

[andywirv]

Fixes #14