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/composables/useSiteMeta.js

@@ -0,0 +1,58 @@
+/**
+ * useSiteMeta — set page-level SEO + social meta with site defaults baked in.
+ *
+ * Builds absolute URLs from runtimeConfig.public.appUrl so og:image and og:url
+ * resolve for crawlers. Defaults og:type=website, twitter:card=summary_large_image,
+ * og:site_name=Ghost Guild. Set noindex:true to emit robots="noindex, nofollow".
+ *
+ * Pass a function (or refs in fields) to keep tags reactive when content loads
+ * asynchronously via useFetch.
+ */
+export function useSiteMeta(input) {
+  const runtimeConfig = useRuntimeConfig()
+  const route = useRoute()
+  const appUrl = (runtimeConfig.public.appUrl || '').replace(/\/$/, '')
+
+  const resolve = () => (typeof input === 'function' ? input() : input) || {}
+
+  const buildAbsolute = (path) => {
+    if (!path) return undefined
+    if (/^https?:\/\//i.test(path)) return path
+    return `${appUrl}${path.startsWith('/') ? '' : '/'}${path}`
+  }
+
+  const titleGetter = () => resolve().title || 'Ghost Guild'
+  const descGetter = () => resolve().description || undefined
+  const isBareTitle = () => Boolean(resolve().bareTitle)
+  const imageGetter = () => buildAbsolute(resolve().image || '/og/default.png')
+  const typeGetter = () => resolve().type || 'website'
+  const robotsGetter = () =>
+    resolve().noindex ? 'noindex, nofollow' : undefined
+  const canonicalGetter = () => buildAbsolute(route.path)
+
+  useSeoMeta({
+    title: titleGetter,
+    description: descGetter,
+    ogSiteName: 'Ghost Guild',
+    ogTitle: titleGetter,
+    ogDescription: descGetter,
+    ogType: typeGetter,
+    ogUrl: canonicalGetter,
+    ogImage: imageGetter,
+    ogImageWidth: 1200,
+    ogImageHeight: 630,
+    twitterCard: 'summary_large_image',
+    twitterTitle: titleGetter,
+    twitterDescription: descGetter,
+    twitterImage: imageGetter,
+    robots: robotsGetter,
+  })
+
+  useHead({
+    link: [{ rel: 'canonical', href: canonicalGetter }],
+  })
+
+  if (isBareTitle()) {
+    useHead({ titleTemplate: null })
+  }
+}