Wake on click instantly instead of the next 0.5s tick

The main loop slept on time.sleep(event_deadline()), so a click sat in
the datagram socket until the next 0.5s timer tick woke the loop. That
added up to ~450ms of latency before the click affected state.json, on
top of waybar's 1s re-poll. Replace the sleep with select() on the
socket: select returns the moment a datagram arrives, so the loop
drains and writes the click within milliseconds (measured 29ms) while
still bounding idle sleep by the next timer deadline. Rotation cadence
and click-during-fetch behavior are unchanged.

The waybar custom-module interval stays 1: fractional intervals below
1s break custom modules (Waybar #4894 turns 0.5 into a 1ms busy loop),
so the 0-1s re-poll is the floor and not safely tunable.

scripts/ocd-waybar

@@ -16,6 +16,7 @@
 import json
 import os
 import re
+import select
 import signal
 import socket
 import subprocess
@@ -451,7 +452,17 @@ def main():
         d.maybe_tick()
         d.drain_socket()
         d.render_and_write()
-        time.sleep(d.event_deadline())
+        # Sleep until the next tick OR a click, whichever is first.
+        # select on the socket lets a click wake the loop at once instead
+        # of waiting up to TICK_SECS for the next timer tick.
+        timeout = d.event_deadline()
+        if d.sock is not None:
+            try:
+                select.select([d.sock], [], [], timeout)
+            except (OSError, ValueError):
+                time.sleep(timeout)
+        else:
+            time.sleep(timeout)
     d.stop()