Add frontend Dockerfile and integrate into docker-compose

- Multi-stage Dockerfile (deps → build → runner) for optimized production image
- Enable Next.js standalone output for minimal container size
- Add .dockerignore to exclude dev artifacts from build context
- Add frontend service to docker-compose.yml with API dependency

https://claude.ai/code/session_01QU6gpDgMtX4b9k1UXTivEf

frontend/.dockerignore

@@ -0,0 +1,7 @@
+node_modules
+.next
+.git
+.gitignore
+*.md
+.env*
+vitest.config.ts