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/series/index.vue

@@ -72,15 +72,10 @@
 </template>
 
 <script setup>
-useHead({
-  title: "Event Series - Ghost Guild",
-  meta: [
-    {
-      name: "description",
-      content:
-        "Multi-session events on cooperative topics for game developers.",
-    },
-  ],
+useSiteMeta({
+  title: "Event Series",
+  description:
+    "Multi-session event series on cooperative topics — from foundations courses to practitioner cohorts.",
 });
 
 const { data: seriesData, pending } = await useFetch("/api/series", {