fix(website): static-site Caddy routing (no SPA fallback)

Replace the SPA try_files fallback with static multi-page routing (resolve each
page's index.html, serve real 404.html) — this is a Starlight static site, so the
old fallback served the landing page for deep links/misses.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Nathan Flurry

frontend/packages/website/Dockerfile

@@ -17,11 +17,18 @@ RUN pnpm build
 
 FROM caddy:alpine
 COPY --from=build /app/dist /srv
+# Static multi-page site (Astro/Starlight emits <path>/index.html), NOT an SPA —
+# resolve each page's index.html and serve the real 404.html on a miss.
 RUN cat > /etc/caddy/Caddyfile <<'EOF'
 :80 {
 	root * /srv
+	encode gzip
+	try_files {path} {path}/index.html {path}.html
 	file_server
-	try_files {path} /index.html
+	handle_errors {
+		rewrite * /404.html
+		file_server
+	}
 }
 EOF
 EXPOSE 80