feat: add Dockerfile for Coolify static deployment

Multi-stage build: Node für SvelteKit build, Nginx zum Ausliefern.
Kopiert build/ nach /usr/share/nginx/html für die Standard-Coolify-Config.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,9 @@
+FROM node:22-alpine AS build
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci
+COPY . .
+RUN npm run build
+
+FROM nginx:alpine
+COPY --from=build /app/build /usr/share/nginx/html