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/privacy.vue

@@ -231,8 +231,10 @@
 </template>
 
 <script setup>
-useHead({
-  title: 'Privacy Policy · Ghost Guild',
+useSiteMeta({
+  title: 'Privacy Policy',
+  description:
+    'How Ghost Guild handles your data: what we collect, why we collect it, and who has access. No Google Analytics, no advertising pixels, no third-party tracking.',
 })
 </script>