migrate from astro+netlify to tanstack start + self-hosted

Replace the Astro static site with a TanStack Start (Bun runtime) app and
add Dockerfile + compose files so the site can be served from home-main-2
behind the home-reverse-proxy-1 Caddy instead of Netlify. CI workflow
rewritten to build a container image and SSH-deploy to the home host.

src/server.tsx

@@ -0,0 +1,7 @@
+import handler from "@tanstack/react-start/server-entry";
+
+export default {
+	fetch(req: Request): Promise<Response> {
+		return handler.fetch(req);
+	},
+};