feat(sitemap): update base URL and add build environment handling

Change the base URL from localhost to the production URL. 
Implement a check for the build environment to use mock data 
for generating the sitemap during the build process. 
This ensures that sitemap is correctly populated 
with project routes even when the API is not available.

Dockerfile

@@ -13,9 +13,15 @@ RUN npm install
 # Copy the application code
 COPY . .
 
+# Set IS_BUILD environment variable for build process
+ENV IS_BUILD=true
+
 # Build the Next.js application
 RUN npm run build
 
+# Unset IS_BUILD environment variable for runtime
+ENV IS_BUILD=false
+
 # Set environmental variable for production mode
 ENV NODE_ENV=production
 
@@ -23,4 +29,4 @@ ENV NODE_ENV=production
 EXPOSE 3000
 
 # Run the app with the start script
-CMD ["npm", "start"]
+CMD ["npm", "start"]s