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/sections/Landing.tsx

@@ -0,0 +1,21 @@
+import LogoQuadBG from "@/components/LogoQuadBG";
+import bgDark from "@/assets/unom_Logo_5_Dark.webp";
+
+export default function Landing() {
+	return (
+		<div className="w-full h-screen object-cover">
+			<div className="w-full h-full flex items-center justify-center absolute">
+				<div className="w-[200px]">
+					<LogoQuadBG />
+				</div>
+			</div>
+			<img
+				className="h-full w-full object-cover"
+				src={bgDark}
+				width={3840}
+				height={2160}
+				alt="Ein 3D Rendering des unom Logos"
+			/>
+		</div>
+	);
+}