feat(seo): site meta composable + Open Graph image generation

Adds `useSiteMeta()` composable that wraps useSeoMeta with site defaults
(title template, canonical URL, og/twitter image, og:site_name) and
absolute-URL handling via runtimeConfig.public.appUrl.

Adds /og/events/[slug].png route that renders per-event OG images via
satori + @resvg/resvg-js, cached on disk by slug + updatedAt. Bundles
Brygada 1918 + Commit Mono fonts as server assets, ships a fallback
default.png, and patches @shuding/opentype.js via patch-package.

Converts ~25 pages from useHead to useSiteMeta and adds noindex on
private/auth/admin pages.

app/pages/policies/[slug].vue

@@ -39,8 +39,9 @@ if (!policy) {
   throw createError({ statusCode: 404, statusMessage: 'Policy not found', fatal: true })
 }
 
-useHead({
-  title: `${policy.title} · Ghost Guild`,
+useSiteMeta({
+  title: policy.title,
+  description: policy.description,
 })
 </script>