fix: Add .dockerignore to exclude Next.js root from Astro build

- Ignore root package.json and Next.js files
- Prevents npm from finding wrong project
- Ensures only Astro code is built

Fixes build error where Next.js code was being compiled.

dealplustech-astro/Dockerfile

@@ -9,7 +9,7 @@ COPY package*.json ./
 # Install dependencies
 RUN npm ci --omit=dev
 
-# Copy source code
+# Copy all source code
 COPY . .
 
 # Build Astro project (includes public folder in dist)