feat: image pipeline with JPEG decode, resize, and Floyd-Steinberg dithering

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

src/image_pipeline.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include <Arduino.h>
+#include "config.h"
+
+struct ProcessedImage {
+    uint8_t* framebuffer;  // Palette indices, one byte per pixel
+    uint16_t width;
+    uint16_t height;
+    bool valid;
+};
+
+class ImagePipeline {
+public:
+    // Process single landscape photo
+    ProcessedImage process(uint8_t* jpegData, size_t jpegSize);
+
+    // Process portrait pair (two photos side by side)
+    ProcessedImage processPortraitPair(uint8_t* jpeg1Data, size_t jpeg1Size,
+                                        uint8_t* jpeg2Data, size_t jpeg2Size);
+
+    void freeImage(ProcessedImage& img);
+
+private:
+    // Decode JPEG into RGB888 buffer in PSRAM
+    uint8_t* decodeJpeg(uint8_t* data, size_t size, uint16_t* outWidth, uint16_t* outHeight);
+
+    // Resize RGB buffer to target dimensions (bilinear)
+    uint8_t* resize(uint8_t* rgb, uint16_t srcW, uint16_t srcH,
+                    uint16_t dstW, uint16_t dstH);
+
+    // Center-crop to target aspect ratio
+    void centerCrop(uint8_t* rgb, uint16_t srcW, uint16_t srcH,
+                    uint16_t targetW, uint16_t targetH,
+                    uint16_t* cropX, uint16_t* cropY,
+                    uint16_t* cropW, uint16_t* cropH);
+
+    // Floyd-Steinberg dither RGB888 to 6-color palette indices
+    uint8_t* dither(uint8_t* rgb, uint16_t width, uint16_t height);
+
+    // Find nearest palette color
+    uint8_t findNearest(int r, int g, int b);
+};