fix(org): favicon fallback, OG logo styling, and Discord embed CDN URLs (#714)

* fix(org): serve OG images from CDN for Discord embeds

Discord times out on slow dynamic OG generation (~3-5s). Persist generated
images to R2, point meta tags at the media CDN, and warm the API endpoint
on org-site page loads so crawlers get a fast static PNG URL.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* docs: add org-site Open Graph and favicon guides

Document user-facing sharing behavior and contributor architecture
for dynamic OG images, favicon fallback, R2/CDN caching, and embed
cache invalidation.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(org-site): address PR review on OG CDN fallback and docs

- Fall back to API OG URL when CDN object is not yet available (HEAD check)
- Cancel warm-fetch response body to avoid connection pool exhaustion
- Align tenant-router OG edge cache TTL with one-hour API revalidation
- Fix favicon docs navigation and add Custom Domain tab screenshot
- Replace Chiberry Artistry example with AI Academy

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

* fix(org-site): accept docker hostnames for OG warm URL

Use isValidHttpUrl for PRIVATE_SERVER_URL so internal values like
http://api:3081 work for SSR warm fetches in Docker Compose.

Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

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Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

apps/dashboard/.env.example

@@ -32,6 +32,8 @@ UNSPLASH_API_KEY=
 # Sever URL - Optional if you want to use video upload and pdf downloads
 # This is the deployment URL of apps/api
 PUBLIC_SERVER_URL=
+# Public CDN base for uploaded media (org OG images are served from /og/{siteName}.png)
+# PUBLIC_MEDIA_CDN_URL=https://img.cdn.clsrio.com
 # Optional server-only override used during SSR (for Docker/internal network)
 # Example in compose: http://api:3081
 PRIVATE_SERVER_URL=