fix(og-image): use slug-only path for OG image URL

OG images are served at /og/{slug}.png (e.g. /og/14b61.png),
not with date prefixes. Remove the date segments from the URL
construction in both jf2ToActivityStreams and jf2ToAS2Activity.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/jf2-to-as2.js

@@ -165,7 +165,7 @@ export function jf2ToActivityStreams(properties, actorUrl, publicationUrl, optio
   if (ogMatch) {
     object.image = {
       type: "Image",
-      url: `${publicationUrl.replace(/\/$/, "")}/og/${ogMatch[2]}-${ogMatch[3]}-${ogMatch[4]}-${ogMatch[5]}.png`,
+      url: `${publicationUrl.replace(/\/$/, "")}/og/${ogMatch[5]}.png`,
       mediaType: "image/png",
     };
   }
@@ -366,7 +366,7 @@ export function jf2ToAS2Activity(properties, actorUrl, publicationUrl, options =
   const ogMatchF = postUrl && postUrl.match(/\/([\w-]+)\/(\d{4})\/(\d{2})\/(\d{2})\/([\w-]+)\/?$/);
   if (ogMatchF) {
     noteOptions.image = new Image({
-      url: new URL(`${publicationUrl.replace(/\/$/, "")}/og/${ogMatchF[2]}-${ogMatchF[3]}-${ogMatchF[4]}-${ogMatchF[5]}.png`),
+      url: new URL(`${publicationUrl.replace(/\/$/, "")}/og/${ogMatchF[5]}.png`),
       mediaType: "image/png",
     });
   }