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>

---------

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

apps/dashboard/src/routes/+layout.server.ts

@@ -2,9 +2,12 @@ import type { AccountOrg } from '$features/app/types';
 import type { MetaTagsProps } from 'svelte-meta-tags';
 import type { UploadLimits } from '$lib/utils/config/upload-limits';
 import { PUBLIC_IS_SELFHOSTED } from '$env/static/public';
+import { env } from '$env/dynamic/private';
+import { env as publicEnv } from '$env/dynamic/public';
 import { getBaseMetaTags } from '$lib/utils/functions/metaTags.server';
 import { getOrgSiteInfo } from '$features/app/layout-setup';
 import { getUploadLimits } from '$lib/utils/config/upload-limits';
+import { resolveOrgSiteOgWarmUrl } from '$lib/utils/functions/org-site-og-url';
 
 export const ssr = true;
 
@@ -28,12 +31,27 @@ export const load = async ({ url, cookies, request, locals }): Promise<LoadOutpu
   const orgSiteInfo = await getOrgSiteInfo(url, cookies);
   const orgSiteInfoMs = Math.round((performance.now() - orgSiteInfoStart) * 100) / 100;
 
+  if (orgSiteInfo.isOrgSite && orgSiteInfo.org?.siteName) {
+    const warmUrl = resolveOrgSiteOgWarmUrl({
+      siteName: orgSiteInfo.org.siteName,
+      isSelfHosted: PUBLIC_IS_SELFHOSTED === 'true',
+      privateServerUrl: env.PRIVATE_SERVER_URL,
+      publicServerUrl: publicEnv.PUBLIC_SERVER_URL
+    });
+
+    if (warmUrl) {
+      void fetch(warmUrl)
+        .then((response) => response.body?.cancel())
+        .catch(() => {});
+    }
+  }
+
   const response: LoadOutput = {
     orgSiteName: orgSiteInfo.orgSiteName,
     isOrgSite: orgSiteInfo.isOrgSite,
     skipAuth: orgSiteInfo.subdomain === 'play' || debugPlay === 'true',
     org: orgSiteInfo.org,
-    baseMetaTags: getBaseMetaTags(url, orgSiteInfo),
+    baseMetaTags: await getBaseMetaTags(url, orgSiteInfo),
     serverLang: request.headers?.get('accept-language') || '',
     localeCookie: cookies.get('classroomio_locale') || '',
     locals,