feat: add configurable image input preprocessing (#2028)

include/stable-diffusion.h

@@ -263,6 +263,11 @@ typedef struct {
     uint8_t* data;
 } sd_image_t;
 
+typedef struct {
+    // Semicolon-separated target=...,key=value rules. NULL preserves defaults.
+    const char* rules;
+} sd_image_preprocess_params_t;
+
 typedef struct {
     sd_image_t* frames;
     int frame_count;
@@ -410,6 +415,7 @@ typedef struct {
     int qwen_image_layers;
     bool circular_x;
     bool circular_y;
+    sd_image_preprocess_params_t image_preprocess;
 } sd_img_gen_params_t;
 
 typedef struct {
@@ -443,6 +449,7 @@ typedef struct {
     sd_hires_params_t hires;
     bool circular_x;
     bool circular_y;
+    sd_image_preprocess_params_t image_preprocess;
 } sd_vid_gen_params_t;
 
 typedef struct sd_ctx_t sd_ctx_t;