Refine large-value tiles and fade Guition backlight in hardware

Large-value (watch) tiles show a small domain icon next to the title, centre
title and value vertically, use a dedicated larger digit font, truncate long
values with dots and keep the unit in its own label. The geometry self-test
checks the unit label too.

The Guition backlight now dims through the LEDC hardware fader (1.5 s to
standby, 80 ms wake) so full LVGL redraws no longer make the transition
stutter; ESPHome's light state is synced after each fade. Firmware 0.2.13;
app 0.2.11 stays compatible. Document the shared build directory pitfall.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

backlight_fade.h

@@ -0,0 +1,6 @@
+#pragma once
+#if __has_include("esphome/components/smart_display/backlight_fade.h")
+#include "esphome/components/smart_display/backlight_fade.h"
+#else
+#include "components/smart_display/backlight_fade.h"
+#endif