fix: eliminate diagonal dither pattern from display driver

Root cause: Panel_ED2208's epd_quality mode applies _dither_row_rgb_pair
(diagonal bias pattern with dither=140) during _exec_transfer(). Since our
ImagePipeline already does proper Floyd-Steinberg dithering, the driver's
additional dithering was creating visible diagonal artifacts.

Fix: setEpdMode(epd_fastest) selects _dither_row_none (clean nearest-color
lookup, no spatial bias). On Panel_ED2208 this only affects the dither
function — NOT refresh quality or waveform.

Also: default dither_noise setting to OFF since error scatter was targeting
the wrong layer (it made gradient areas fuzzier without fixing the real
problem in the display driver).

Co-authored-by: Cursor <cursoragent@cursor.com>

src/power_manager.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <Arduino.h>
+#include <esp_sleep.h>
 #include "config.h"
 
 class PowerManager {
@@ -10,11 +11,14 @@ public:
     bool isCharging();
     void updateBatteryLED();
     void flashLED(uint8_t r, uint8_t g, uint8_t b, uint16_t duration_ms = LED_PULSE_DURATION_MS);
-    void enterDeepSleep();
+    void enterDeepSleep(uint32_t sleepMinutes = 0);
     void enableLightSleep();
     void disableEPDPower();
     void enableEPDPower();
 
+    static bool wasTimedSleepWake();
+    static void clearTimedSleepFlag();
+
 private:
     uint8_t _lastBatteryPct = 100;
     unsigned long _lastLEDPulse = 0;