feat: add backend image transform types with crop support

backend/src/types/image.ts

@@ -0,0 +1,23 @@
+export type OutputFormat = "png" | "webp" | "jpeg";
+
+export type FitMode = "inside" | "outside" | "cover" | "contain";
+
+export type CropPosition =
+  | "center"
+  | "top"
+  | "right"
+  | "bottom"
+  | "left"
+  | "top-left"
+  | "top-right"
+  | "bottom-left"
+  | "bottom-right";
+
+export interface TransformRequest {
+  width?: number;
+  height?: number;
+  quality?: number;
+  format?: OutputFormat;
+  fit?: FitMode;          // "inside" = resize only, "cover" = crop to fill
+  position?: CropPosition; // crop anchor when using cover
+}