Initial fullstack project setup with Next.js 15, Gin, PostgreSQL and Docker Compose

- Frontend: Next.js 15 (App Router), Auth.js v5, shadcn/ui, MagicUI
- Backend: Go + Gin + GORM with layered architecture
- Auth: Local credentials login with optional Keycloak OAuth binding
- Admin: RBAC user management for admin role
- Dev: Docker Compose with hot reload for both frontend and backend
- Docker: 3-service orchestration (frontend, backend, postgres)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

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