feat: Fase 1 – Fondamenta complete (backend FastAPI + auth + permessi)

- docker-compose.yml: PostgreSQL 16, Redis 7, MinIO, Nginx
- backend FastAPI: struttura monorepo, config pydantic-settings
- modelli SQLAlchemy: tutti i modelli (tenants, users, mailboxes, messages, archival, permissions, labels, audit_log)
- migrazione Alembic 0001: schema completo in pure SQL
- auth API: login JWT, refresh token rotation, logout, 2FA TOTP (setup/verify/disable)
- CRUD utenti: lista, crea, modifica, reset password, soft delete
- permessi granulari (Fase 1-A): mailbox_permissions, assegna/revoca/lista
- CRUD tenant: gestione super-admin
- sicurezza: AES-256-GCM cifratura credenziali IMAP/SMTP, bcrypt password
- RLS PostgreSQL: isolamento multi-tenant per request
- seed sviluppo: tenant demo + admin + operator
- test unit: security (bcrypt, JWT, AES), auth_service
- test integration: auth endpoints, users endpoints
- CI GitHub Actions: lint (ruff), test (pytest), build Docker, security scan
- infra: nginx.conf, redis.conf
- Makefile con comandi make dev/test/migrate/seed

Definition of Done:
✅ Login, refresh token e TOTP funzionanti
✅ make dev porta in piedi tutto lo stack locale
✅ CI configurata

infra/nginx/nginx.conf

@@ -0,0 +1,45 @@
+user  nginx;
+worker_processes  auto;
+error_log  /var/log/nginx/error.log warn;
+pid        /var/run/nginx.pid;
+
+events {
+    worker_connections  1024;
+    use epoll;
+    multi_accept on;
+}
+
+http {
+    include       /etc/nginx/mime.types;
+    default_type  application/octet-stream;
+
+    # Logging format
+    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
+                      '$status $body_bytes_sent "$http_referer" '
+                      '"$http_user_agent" "$http_x_forwarded_for"';
+    access_log  /var/log/nginx/access.log  main;
+
+    # Performance
+    sendfile        on;
+    tcp_nopush      on;
+    tcp_nodelay     on;
+    keepalive_timeout  65;
+    gzip            on;
+    gzip_types      text/plain text/css application/json application/javascript
+                    text/xml application/xml application/xml+rss text/javascript;
+
+    # Security headers
+    add_header X-Content-Type-Options nosniff;
+    add_header X-Frame-Options DENY;
+    add_header X-XSS-Protection "1; mode=block";
+    add_header Referrer-Policy "strict-origin-when-cross-origin";
+
+    # Hide nginx version
+    server_tokens off;
+
+    # Rate limiting zones
+    limit_req_zone $binary_remote_addr zone=auth:10m rate=10r/m;
+    limit_req_zone $binary_remote_addr zone=api:10m rate=100r/m;
+
+    include /etc/nginx/conf.d/*.conf;
+}