Add Docker infrastructure with caddy-docker-proxy

Multi-stage Dockerfile (node build → caddy:2-alpine production, node dev).
Compose base + dev override for prod/dev switching via .env ENVIRONMENT flag.
Makefile targets: build, up, down, restart, logs, dev, prod, clean, rebuild.
Caddyfile serves static Astro output with caching and compression.

docker-compose.dev.yml

@@ -0,0 +1,21 @@
+services:
+  docs:
+    build:
+      target: dev
+    volumes:
+      - ./src:/app/src
+      - ./public:/app/public
+      - ./astro.config.mjs:/app/astro.config.mjs
+    environment:
+      - VITE_HMR_HOST=${DOMAIN}
+    labels:
+      caddy: ${DOMAIN}
+      caddy.reverse_proxy: "{{upstreams 4321}}"
+      caddy.reverse_proxy.flush_interval: "-1"
+      caddy.reverse_proxy.transport: http
+      caddy.reverse_proxy.transport.read_timeout: "0"
+      caddy.reverse_proxy.transport.write_timeout: "0"
+      caddy.reverse_proxy.transport.keepalive: 5m
+      caddy.reverse_proxy.transport.keepalive_idle_conns: "10"
+      caddy.reverse_proxy.stream_timeout: 24h
+      caddy.reverse_proxy.stream_close_delay: 5s