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.

Dockerfile

@@ -0,0 +1,38 @@
+# --- Build stage ---
+FROM node:22-slim AS build
+
+WORKDIR /app
+
+# Install dependencies first (layer caching)
+COPY package.json package-lock.json ./
+RUN npm ci
+
+# Copy source and build
+COPY . .
+ENV ASTRO_TELEMETRY_DISABLED=1
+RUN npm run build
+
+# --- Production stage ---
+FROM caddy:2-alpine AS production
+
+COPY --from=build /app/dist /srv
+COPY Caddyfile /etc/caddy/Caddyfile
+
+EXPOSE 80
+
+HEALTHCHECK --interval=30s --timeout=3s --start-period=5s \
+  CMD wget -qO- http://127.0.0.1:80/ || exit 1
+
+# --- Dev stage ---
+FROM node:22-slim AS dev
+
+WORKDIR /app
+
+COPY package.json package-lock.json ./
+RUN npm ci
+
+ENV ASTRO_TELEMETRY_DISABLED=1
+
+EXPOSE 4321
+
+CMD ["npm", "run", "dev", "--", "--host", "0.0.0.0"]