* ♻️ use Single Responsibility Principle on brains_subscription
* ✨ new brain subscription endpoints for invited user
* 📝 add documentation to endpoints
* 🎨 add base_frontend_url to send custom url for brain share
* ✏️ brains instead of brain in url
* ✨ use origin in header for frontend url in subscription email
* 🚚 move and remove unused code
* ✨ new subscription API for BE endpoints in frontend
* ✨ new addBrain to add a shared brain in frontend
* 🥚 new hook for brain invitations
* ✨ new page for brain invitation
* ✨ change frontend url to copy for brain subscription
* ✏️ call RBAC with wrapper function
* ✏️ last typos
