refactor: optimize Docker deployment with standalone mode

- Enable Next.js standalone output for smaller image size
- Remove unnecessary npm install in production stage
- Use direct node execution instead of npm start
- Add .dockerignore to exclude unnecessary files from build context

.dockerignore

@@ -0,0 +1,10 @@
+node_modules
+.next
+.git
+.gitignore
+.claude
+*.md
+.env*.local
+npm-debug.log*
+yarn-debug.log*
+yarn-error.log*