feat: add favicons, navbar logo, and OG image

Generate favicon set from devrail-icon.png for all sizes Docsy
references. Add logo.svg to assets/icons/ for navbar. Set OG image
in hugo.toml for social link previews.

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

Author: matthew-on-git

assets/icons/logo.svg

@@ -16,6 +16,7 @@ languageCode = "en-us"
   github_repo = "https://github.com/devrail-dev/devrail.dev"
   github_project_repo = "https://github.com/devrail-dev"
   offlineSearch = false
+  images = ["images/devrail-icon.png"]
 
 [[params.links.developer]]
   name = "GitHub"