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/accept-invite.vue

@@ -242,6 +242,7 @@ import {
 } from "~/config/contributions";
 
 definePageMeta({ layout: false });
+useSiteMeta({ title: "Accept Invitation", noindex: true });
 
 const { checkMemberStatus } = useAuth();
 const { initializeHelcimPay, verifyPayment } = useHelcimPay();