feat(frontend): replace placeholder avatar with identicons

i don't actually know what the license on the kitten image is, and while
it's very unlikely, i don't want to get into legal trouble. it was only
ever supposed to be a temporary image, too.

identicons aren't the prettiest but at least they have a clear license
:3

Foxnouns.Frontend/package.json

@@ -42,6 +42,7 @@
 		"bootstrap-icons": "^1.11.3",
 		"luxon": "^3.5.0",
 		"markdown-it": "^14.1.0",
+		"minidenticons": "^4.2.1",
 		"pretty-bytes": "^6.1.1",
 		"sanitize-html": "^2.13.1",
 		"svelte-tippy": "^1.3.2",