refactor: Move Astro project to root directory

- Move all Astro files from dealplustech-astro/ to root
- Archive Next.js code in _nextjs-backup/
- Update .gitignore for Astro project
- Simplify project structure

This completes the migration from Next.js to Astro.
The Astro project is now at the root level.

Dockerfile

@@ -0,0 +1,22 @@
+# Astro Production Dockerfile
+FROM node:20-alpine
+
+WORKDIR /app
+
+# Copy package files
+COPY package*.json ./
+
+# Install dependencies
+RUN npm ci --omit=dev
+
+# Copy all source code
+COPY . .
+
+# Build Astro project (includes public folder in dist)
+RUN npm run build
+
+# Expose port
+EXPOSE 4321
+
+# Start Astro preview server
+CMD ["npm", "run", "preview", "--", "--host", "0.0.0.0", "--port", "4321"]