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.

.dockerignore

@@ -0,0 +1,16 @@
+node_modules
+.output
+.nitro
+.tanstack
+dist
+.git
+.gitea
+.github
+.idea
+.vscode
+.DS_Store
+.env
+.env.*
+*.log
+bun-debug.log*
+README.md