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

frontend/public/icons/icon.svg

@@ -0,0 +1,6 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512" role="img" aria-label="NexaPantry">
+  <rect width="512" height="512" rx="96" fill="#0f766e"/>
+  <path fill="#f8fafc" d="M150 152h212l-18 248H168l-18-248Zm34 40 12 168h120l12-168H184Z"/>
+  <path fill="#d9f99d" d="M198 126c24-42 78-54 116-20-16 46-70 64-116 20Z"/>
+</svg>
+