fix: Add .docker/Dockerfile as explicit override for Easypanel

- Create .docker/Dockerfile
- This is a standard location that Easypanel recognizes
- Overrides nixpacks auto-generation
- Simple Astro build without Next.js caching

dealplustech-astro/.docker/Dockerfile

@@ -0,0 +1,14 @@
+# Astro Production Dockerfile
+FROM node:20-alpine
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm ci --omit=dev
+
+COPY . .
+RUN npm run build
+
+EXPOSE 4321
+
+CMD ["npm", "run", "preview", "--", "--host", "0.0.0.0", "--port", "4321"]