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/join.vue

@@ -391,6 +391,12 @@ import {
   getGuidanceLabel,
 } from "~/config/contributions";
 
+useSiteMeta({
+  title: "Join",
+  description:
+    "Join Ghost Guild — a membership community for game developers exploring cooperative models. Everyone gets everything. Pay what you can, $0 to $50 per month.",
+});
+
 // Auth state
 const { isAuthenticated, memberData, checkMemberStatus } = useAuth();