fix: normalize model-visible images with Pi processing

src/agent/image-processing/mime.d.mts

@@ -0,0 +1,3 @@
+import type { SupportedImageMimeType } from "./types.ts";
+export function detectSupportedImageMimeType(buffer: Uint8Array): SupportedImageMimeType | null;
+export function detectSupportedImageMimeTypeFromFile(filePath: string): Promise<SupportedImageMimeType | null>;