Mobile GitHub site support for og:image thumbnails

[dan-ignat]

The og:image functionality added for #612 works great, but it doesn't seem to work at all on the mobile GitHub site.

I sent a GitHub repo URL (which has an image set on its Settings page) from one iPhone to another via iMessage, and it didn't unfurl. I dug into it a bit, using Chrome's DevTools to view my GitHub repo as a mobile device. This let me view the source HTML, and I confirmed that the og:* tags do not appear in the HTML sent to clients by the mobile GitHub site. (I also did a negative test, to confirm that the tags do appear on the regular GitHub site.)

So this means that any repo links sent on mobile devices will not unfurl. It would be nice to fix this, so that GitHub links sent on mobile devices can look as nice as those posted to social media sites.

[Soneji]

+1 I would also like to see this. It's pretty annoying that it doesnt show previews on iMessage!