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]>

apps/tenant-router/src/index.ts

@@ -323,6 +323,7 @@ export default {
 
     const upstreamHost = isApiCall ? env.API_UPSTREAM_HOST : env.DASHBOARD_UPSTREAM_HOST;
     const upstreamPath = isProxiedApiCall ? url.pathname.slice(PROXY_PREFIX.length) || '/' : url.pathname;
+    const isOrgSiteOgImage = isProxiedApiCall && upstreamPath.startsWith('/org-site/og/');
 
     const upstreamUrl = new URL(request.url);
     upstreamUrl.protocol = 'https:';
@@ -346,13 +347,14 @@ export default {
     // cold browser cache (new device, or post-deploy hash change) stampedes the
     // origin for every chunk.
     const isImmutableAsset = url.pathname.startsWith('/_app/immutable/');
+    const edgeCacheTtl = isImmutableAsset ? 31536000 : isOrgSiteOgImage ? 3600 : undefined;
 
     const upstreamResponse = await fetch(upstreamUrl.toString(), {
       method: request.method,
       headers: upstreamHeaders,
       body: request.body,
       redirect: 'manual',
-      cf: isImmutableAsset ? { cacheEverything: true, cacheTtl: 31536000 } : undefined
+      cf: edgeCacheTtl ? { cacheEverything: true, cacheTtl: edgeCacheTtl } : undefined
     });
 
     if (isImmutableAsset) {
@@ -361,6 +363,12 @@ export default {
       return response;
     }
 
+    if (isOrgSiteOgImage && upstreamResponse.ok) {
+      const response = new Response(upstreamResponse.body, upstreamResponse);
+      response.headers.set('Cache-Control', 'public, max-age=3600, stale-while-revalidate=86400');
+      return response;
+    }
+
     return upstreamResponse;
   }
 } satisfies ExportedHandler<Env>;