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 <[email protected]>

* 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 <[email protected]>

* 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 <[email protected]>

* 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 <[email protected]>

---------

Co-authored-by: Cursor Agent <[email protected]>
Co-authored-by: Rotimi Best <[email protected]>

packages/utils/src/org-site/og-public-url.ts

@@ -0,0 +1,11 @@
+export function getOrgSiteOgObjectKey(siteName: string): string {
+  return `og/${encodeURIComponent(siteName)}.png`;
+}
+
+export function buildOrgSiteOgCdnUrl(siteName: string, cdnBaseUrl: string): string {
+  return `${cdnBaseUrl.replace(/\/$/, '')}/${getOrgSiteOgObjectKey(siteName)}`;
+}
+
+export function buildOrgSiteOgApiUrl(siteName: string, apiBaseUrl: string): string {
+  return `${apiBaseUrl.replace(/\/$/, '')}/org-site/og/${encodeURIComponent(siteName)}.png`;
+}