The synchronous `get_message_from_editor` blocked the main loop (`prof_run`) while launching an external editor like `vim`, halting network I/O in `session_process_events` and preventing incoming message reception.
Introduced `get_message_from_editor_async` for `cmd_editor` to run the editor asynchronously. It forks and execs the editor in a thread (`editor_thread`), suspending NCurses to free the terminal. The main loop skips `inp_readline` and `ui_update` via a new `background_mode` flag while the editor runs, allowing `session_process_events` to keep the connection alive.
On editor completion, `editor_process` (called per loop iteration) resumes NCurses with `ui_resize`, inserts the result into the readline buffer and clears `background_mode`.
Retained synchronous `get_message_from_editor` for ~20 existing code paths (e.g., `vcard_nickname`) to avoid breaking them.
Tested with `vim` and `nano`: confirms no rendering conflicts, messages received during editing, and seamless resume. Edge cases like editor crashes handled via error logging and seamless resume.
