chore: initial project setup with backend, frontend, and infrastructure

Add complete NexaPantry application structure including:
- Docker Compose configuration with PostgreSQL, Redis, FastAPI backend, worker, frontend and Caddy
- Environment configuration template with database, auth, and service settings
- GitHub Actions CI workflow for backend/frontend linting, testing, auditing and Docker builds
- AGPL-3.0 license and comprehensive README with setup, development, and security documentation
- Backend

.env.example

@@ -0,0 +1,16 @@
+COMPOSE_PROJECT_NAME=nexapantry
+APP_ENV=production
+INSTANCE_URL=http://localhost
+FRONTEND_ORIGIN=http://localhost
+POSTGRES_DB=nexapantry
+POSTGRES_USER=nexapantry
+POSTGRES_PASSWORD=change-me-long-random-password
+DATABASE_URL=postgresql+psycopg://nexapantry:change-me-long-random-password@postgres:5432/nexapantry
+REDIS_URL=redis://redis:6379/0
+JWT_SECRET_KEY=change-me-at-least-32-random-bytes-before-production
+SETTINGS_SECRET_KEY=aXJQnbHFP0V7nCyhSEmqktlCREo21daLKs6dK7Pf3Uw=
+COOKIE_SECURE=false
+CORS_ORIGINS=http://localhost,http://localhost:5173
+LOG_LEVEL=INFO
+DEFAULT_TIMEZONE=Europe/Vienna
+DAILY_WORKER_INTERVAL_SECONDS=300