feat: add Docker deployment (Dockerfile, compose, Caddyfile)

Multi-stage Dockerfile builds SvelteKit then runs a lean production image. docker-compose.yml wires up MariaDB with health checks, the app, and Caddy for TLS termination. Caddyfile uses SITE_DOMAIN env var with localhost fallback.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,18 @@
+FROM node:22-alpine AS builder
+WORKDIR /app
+COPY package*.json ./
+RUN npm ci
+COPY . .
+RUN npm run build
+
+FROM node:22-alpine
+WORKDIR /app
+COPY --from=builder /app/build ./build
+COPY --from=builder /app/node_modules ./node_modules
+COPY --from=builder /app/package.json ./
+COPY --from=builder /app/drizzle ./drizzle
+COPY --from=builder /app/scripts ./scripts
+
+ENV NODE_ENV=production
+EXPOSE 3000
+CMD ["node", "build"]