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.

server/routes/og/events/[slug].js

@@ -0,0 +1,29 @@
+// GET /og/events/[slug].png — generated Open Graph image for an event.
+// Cached on disk by slug + event.updatedAt so any admin edit busts the cache.
+
+export default defineEventHandler(async (event) => {
+  const slug = getRouterParam(event, 'slug')
+  if (!slug) {
+    throw createError({ statusCode: 400, statusMessage: 'Missing slug' })
+  }
+
+  // .png suffix is part of the route filename, but slugs in DB don't include it.
+  const cleanSlug = slug.replace(/\.png$/, '')
+
+  const eventDoc = await loadPublicEvent(event, cleanSlug, { lean: true })
+  const key = eventCacheKey(eventDoc)
+
+  let png = await getCachedOG(key)
+  if (!png) {
+    png = await renderEventOG(eventDoc)
+    await setCachedOG(key, png)
+  }
+
+  setHeader(event, 'Content-Type', 'image/png')
+  setHeader(
+    event,
+    'Cache-Control',
+    'public, max-age=3600, s-maxage=86400, stale-while-revalidate=86400'
+  )
+  return png
+})