Schedule pages and rotation rules can be skipped in slow mode

Each page in a schedule block, and each rule that adds its page to the
rotation, has a "skip in slow mode" checkbox. While slow mode is on those
pages are left out of the rotation; when none of the block's pages are
left, the chosen page is shown. The rotation keeps its own timers.

Schedule format version 5; version 4 is converted when read and stored
again in version 5 on the next save.

Version 2.18.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/home-assistant.md

@@ -26,7 +26,8 @@ The ESP32 connects to Home Assistant in two ways:
 - `FlipDot Display Slow mode` switch and `FlipDot Display Slow mode interval` dropdown
   (`1 minute` ... `60 minutes`): the display only changes at those times, on the clock, and
   is switched off in between (less noise, e.g. in the evening with an automation). Rules
-  with "show at once in slow mode" still show their page right away.
+  with "show at once in slow mode" still show their page right away; pages with "skip in
+  slow mode" are left out of the rotation.
 - `FlipDot Display Firmware` sensor: version and health, e.g. `2.7.2, ok, 0 crashes, recovery ok`.
 - `FlipDot Display Recovery` button: restarts into the [recovery app](recovery.md) for 10
   minutes.