Add complete database schema and ORM models (#4)

internal/models/session.go

@@ -0,0 +1,27 @@
+package models
+
+import (
+	"context"
+	"fmt"
+	"time"
+)
+
+// Session represents a server-held user session.
+type Session struct {
+	Base
+
+	ID           string     `json:"id"`
+	UserID       string     `json:"userId"`
+	CreatedAt    time.Time  `json:"createdAt"`
+	LastActiveAt time.Time  `json:"lastActiveAt"`
+	ExpiresAt    *time.Time `json:"expiresAt,omitempty"`
+}
+
+// User returns the user who owns this session.
+func (s *Session) User(ctx context.Context) (*User, error) {
+	if ul := s.GetUserLookup(); ul != nil {
+		return ul.GetUserByID(ctx, s.UserID)
+	}
+
+	return nil, fmt.Errorf("user lookup not available")
+}