flutter 상위 구조로 포함. infra 분리 리팩토링

.gitignore

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+# General
+.env
+.DS_Store
+.idea/
+.vscode/
+*.swp
+*.log
+
+# Docker Services Data (Volumes)
+postgres_data/
+clickhouse_data/
+
+# Backend (Go)
+backend/main
+backend/bin/
+backend/vendor/
+backend/tmp/
+backend/.env
+
+# Frontend (Flutter)
+# Note: Frontend might have its own .gitignore, but adding here just in case
+frontend/build/
+frontend/.dart_tool/
+frontend/.packages
+frontend/.pub/
+frontend/.env