Slow mode replaces the late-evening quarter hours

Slow mode (Home Assistant switch "FlipDot Display Slow mode", dropdown
"FlipDot Display Slow mode interval", web UI Settings) makes the display
change only every 1, 2, 5, 10, 15, 20, 30 or 60 minutes, on the clock, and
powers it off in between: less noise. Nothing else is drawn meanwhile, also
no page changes. It updates at once after boot, the night, the Power switch
and live mode, and when it is switched off. Rules can override it ("show at
once in slow mode"): while their page is shown the display works normally.

Settings layout 7 and schedule layout 4 (older records are converted; they
are stored again once the firmware is marked good, so a rollback still
finds the old ones). Pages in older formats are rewritten in the current
one, in time-boxed steps. /api/status reports old_data_left.

Version 2.15.0.

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

docs/home-assistant.md

@@ -23,6 +23,10 @@ The ESP32 connects to Home Assistant in two ways:
   stopwatch of the dynamic pages.
 - `FlipDot Display Shown page` sensor: what the display shows now (schedule, rule or
   chosen page). `FlipDot Display Back to schedule` button: ends a page chosen by hand.
+- `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.
 - `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.