un-hardcoded jpg, switch to webp in a few cases

bskyogcard/src/components/Img.tsx

@@ -1,10 +1,21 @@
 import React from 'react'
 
+function detectMime(buf: Buffer): string {
+  if (buf[0] === 0xff && buf[1] === 0xd8) return 'image/jpeg'
+  if (buf[0] === 0x89 && buf[1] === 0x50) return 'image/png'
+  if (buf[0] === 0x52 && buf[1] === 0x49) return 'image/webp'
+  if (buf[0] === 0x47 && buf[1] === 0x49) return 'image/gif'
+  return 'image/jpeg'
+}
+
 export function Img(
   props: Omit<React.ImgHTMLAttributes<HTMLImageElement>, 'src'> & {src: Buffer},
 ) {
   const {src, ...others} = props
   return (
-    <img {...others} src={`data:image/jpeg;base64,${src.toString('base64')}`} />
+    <img
+      {...others}
+      src={`data:${detectMime(src)};base64,${src.toString('base64')}`}
+    />
   )
 }