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>

components/smart_display/backlight_fade.h

@@ -0,0 +1,60 @@
+#pragma once
+#include <algorithm>
+#include <cmath>
+#include <driver/ledc.h>
+#include "esphome/components/ledc/ledc_output.h"
+#include "esphome/components/light/light_state.h"
+
+// Backlight fades through the LEDC hardware fader. ESPHome's software
+// transition steps the duty from the main loop, and the full LVGL redraws that
+// standby triggers on the Guition's RGB panel stall that loop long enough to
+// make dimming visibly jerky. The peripheral steps on its own clock instead.
+namespace backlight_fade {
+template<typename T> struct Peek : T {
+  static uint8_t channel(T &o) { return o.*(&Peek::channel_); }
+  static uint8_t bits(T &o) { return o.*(&Peek::bit_depth_); }
+};
+inline bool installed = false, hardware_owns = false;
+inline ledc_mode_t mode(uint8_t channel) {
+#ifdef SOC_LEDC_SUPPORT_HS_MODE
+  return channel < 8 ? LEDC_HIGH_SPEED_MODE : LEDC_LOW_SPEED_MODE;
+#else
+  return LEDC_LOW_SPEED_MODE;
+#endif
+}
+// Returns false when the fader is unavailable; the caller keeps ESPHome's transition.
+inline bool start(esphome::ledc::LEDCOutput &output, esphome::light::LightState &light, float level, uint32_t ms) {
+#ifndef SOC_LEDC_SUPPORT_FADE_STOP
+  return false;  // Classic ESP32 cannot interrupt a running fade for a touch wake.
+#else
+  using P = Peek<esphome::ledc::LEDCOutput>;
+  const auto channel = static_cast<ledc_channel_t>(P::channel(output));
+  const uint8_t bits = P::bits(output);
+  if (!bits) return false;
+  if (!installed) installed = ledc_fade_func_install(0) == ESP_OK;
+  if (!installed) return false;
+  const auto speed = mode(channel);
+  const uint32_t max_duty = (1u << bits) - 1;
+  ledc_fade_stop(speed, channel);
+  // ESPHome parks 0 % and 100 % with ledc_stop and leaves a stale duty register.
+  // Restart the channel at the level it believes, unless a fade already owns it.
+  float current = 0;
+  light.current_values_as_brightness(&current);
+  const uint32_t from = hardware_owns ? ledc_get_duty(speed, channel) : static_cast<uint32_t>(std::lround(current * max_duty));
+  ledc_set_duty(speed, channel, from);
+  ledc_update_duty(speed, channel);
+  hardware_owns = true;
+  const auto target = static_cast<uint32_t>(std::lround(light.gamma_correct_lut(std::clamp(level, 0.0f, 1.0f)) * max_duty));
+  return ledc_set_fade_with_time(speed, channel, target, ms) == ESP_OK &&
+         ledc_fade_start(speed, channel, LEDC_FADE_NO_WAIT) == ESP_OK;
+#endif
+}
+// Hand the finished level back to ESPHome so HA and later transitions start from the truth.
+inline void sync(esphome::ledc::LEDCOutput &output, esphome::light::LightState &light, float level) {
+#ifdef SOC_LEDC_SUPPORT_FADE_STOP
+  if (hardware_owns) ledc_fade_stop(mode(Peek<esphome::ledc::LEDCOutput>::channel(output)), static_cast<ledc_channel_t>(Peek<esphome::ledc::LEDCOutput>::channel(output)));
+#endif
+  light.turn_on().set_transition_length(0).set_brightness(std::clamp(level, 0.0f, 1.0f)).perform();
+  hardware_owns = false;
+}
+}  // namespace backlight_fade