refactor: use EPD-exact bgr888 palette with bulk pushImage

Replace the PALETTE_565 + writePixel loop with a bgr888_t palette whose
values exactly match Panel_ED2208's internal epd_palette, pushed via a
single pushImage() call.

Benefits:
- Eliminates ~240K individual writePixel calls per frame
- Zero-distance palette values guarantee correct color mapping
- Removes lossy RGB565 intermediate encoding
- Remove unused paletteToColor565() helper

Also adds informational comment to triggerRefresh() noting that
Panel_ED2208::_exec_transfer always sends the full 400x600 frame.

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

src/display_manager.cpp

@@ -2,14 +2,16 @@
 #include "power_manager.h"
 #include <M5Unified.h>
 
-// Map 6-color palette indices to RGB565 for M5GFX
-static const uint16_t PALETTE_565[6] = {
-    0x0000,  // Black
-    0xFFFF,  // White
-    0xF800,  // Red (approximate)
-    0x07E0,  // Green (approximate)
-    0x001F,  // Blue (approximate)
-    0xFFE0   // Yellow (approximate)
+// EPD-exact palette: values produce distance=0 in Panel_ED2208's
+// _rgb_to_epd_color nearest-color lookup, guaranteeing correct mapping.
+// Order matches our pipeline's palette indices (0=black..5=yellow).
+static const lgfx::bgr888_t EPD_PALETTE[6] = {
+    {0, 0, 0},         // Black  (EPD_BLACK)
+    {255, 255, 255},   // White  (EPD_WHITE)
+    {191, 0, 0},       // Red    (EPD_RED)
+    {67, 138, 28},     // Green  (EPD_GREEN)
+    {100, 64, 255},    // Blue   (EPD_BLUE)
+    {255, 243, 56}     // Yellow (EPD_YELLOW)
 };
 
 void DisplayManager::begin(PowerManager& power) {
@@ -92,14 +94,10 @@ void DisplayManager::showImage(const ProcessedImage& img) {
 
     Serial.println("[display] Writing framebuffer to e-ink...");
 
-    // Write pixel by pixel using palette-mapped colors
+    // Bulk-write framebuffer using palette lookup (handles rotation internally)
     _display->startWrite();
-    for (uint16_t y = 0; y < img.height; y++) {
-        for (uint16_t x = 0; x < img.width; x++) {
-            uint8_t colorIdx = img.framebuffer[y * img.width + x];
-            _display->writePixel(x, y, PALETTE_565[colorIdx]);
-        }
-    }
+    _display->pushImage(0, 0, img.width, img.height,
+        img.framebuffer, lgfx::color_depth_t::palette_8bit, EPD_PALETTE);
     _display->endWrite();
     // Do NOT refresh here — caller should add metadata overlay then call refresh()
 }
@@ -361,12 +359,9 @@ void DisplayManager::refresh() {
 }
 
 void DisplayManager::triggerRefresh() {
-    // M5GFX handles e-ink refresh internally when using the EPD panel driver
-    // The display() call triggers the actual e-ink refresh cycle (10-20s)
+    // Panel_ED2208::_exec_transfer always sends the full 400x600 frame
+    // regardless of dirty region — the dirty rect only gates whether
+    // a transfer happens at all. ~30ms at 4MHz SPI, fine for photo frame.
     _display->display();
 }
 
-uint16_t DisplayManager::paletteToColor565(uint8_t index) {
-    if (index >= DISPLAY_COLORS) return 0;
-    return PALETTE_565[index];
-}

src/display_manager.h

@@ -31,5 +31,4 @@ private:
 
     void drawBadge(uint16_t x, uint16_t y, uint16_t w, uint16_t h);
     void triggerRefresh();
-    uint16_t paletteToColor565(uint8_t index);
 };