chore: restructure project into backend and frontend folders

- Move all frontend code to frontend/ directory
- Add backend/ with Go project structure (cmd, internal, pkg)
- Add docker-compose.yml for orchestration

frontend/.dockerignore

@@ -0,0 +1,17 @@
+node_modules
+npm-debug.log
+yarn-error.log
+dist
+.git
+.gitignore
+README.md
+.env
+.env.local
+.DS_Store
+.vscode
+.idea
+*.md
+Dockerfile
+docker-compose.yml
+.dockerignore
+nginx.conf