The IPC event thread had no reconnect: on POLLHUP/POLLERR/POLLNVAL or
read()==0/error it broke out of the loop and the thread exited
permanently, freezing every mango module with stale content until
Waybar was restarted. Wrap the connect + poll/read loop in a reconnect
loop with a bounded 2s backoff, re-establishing the socket and resuming
on disconnect, modeled on the niri backend.
Add an atomic running_ flag so the worker exits cleanly on teardown;
the destructor now sets it false before closing the socket so the
worker breaks out and joins, and leaves the final close to the
destructor to avoid a double close.
Alex