feat: initial commit — backend API + student cabinet frontend

- Go backend: auth (JWT), points earn/spend, QR token generation,
  partners, admin grant/stats endpoints with chi router
- Next.js 14 frontend: login, student dashboard, transaction history,
  QR display, partners list
- PostgreSQL migrations (4 tables), Redis cache, Docker Compose
- CORS middleware, role-based route protection, Zustand auth store

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

backend/internal/admin/service.go

@@ -0,0 +1,167 @@
+package admin
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+
+	"github.com/cu-points/backend/internal/points"
+)
+
+// Service handles business logic for administrative operations.
+type Service struct {
+	db     *pgxpool.Pool
+	points *points.Service
+}
+
+// NewService creates a new admin Service.
+// pointsSvc is used for all balance mutations so that earn logic is not duplicated here.
+func NewService(db *pgxpool.Pool, pointsSvc *points.Service) *Service {
+	return &Service{db: db, points: pointsSvc}
+}
+
+// AdminTransaction is a transaction record as seen by an administrator.
+// It includes the associated user email for quick identification.
+type AdminTransaction struct {
+	ID          string `json:"id"`
+	UserID      string `json:"user_id"`
+	UserEmail   string `json:"user_email"`
+	PartnerID   string `json:"partner_id,omitempty"`
+	Amount      int    `json:"amount"`
+	Type        string `json:"type"`
+	Description string `json:"description,omitempty"`
+	CreatedAt   string `json:"created_at"`
+}
+
+// Student is a user record as seen by an administrator.
+type Student struct {
+	ID        string `json:"id"`
+	Email     string `json:"email"`
+	Name      string `json:"name"`
+	StudentID string `json:"student_id,omitempty"`
+	Balance   int    `json:"balance"`
+}
+
+// Stats holds aggregated system metrics shown on the admin dashboard.
+type Stats struct {
+	TotalStudents     int `json:"total_students"`
+	TotalPointsIssued int `json:"total_points_issued"`
+	TotalPointsSpent  int `json:"total_points_spent"`
+	ActivePartners    int `json:"active_partners"`
+}
+
+// GrantPoints credits the given amount to the student's balance and records an
+// admin_grant transaction. Delegates to points.Service.EarnPoints so that all
+// balance mutation logic lives in one place.
+func (s *Service) GrantPoints(ctx context.Context, userID string, amount int, description string) error {
+	return s.points.EarnPoints(ctx, points.EarnRequest{
+		UserID:      userID,
+		Amount:      amount,
+		Type:        "admin_grant",
+		Description: description,
+	})
+}
+
+// ListTransactions returns a paginated slice of all transactions in the system
+// (newest first) and the total row count for pagination metadata.
+func (s *Service) ListTransactions(ctx context.Context, limit, offset int) ([]AdminTransaction, int, error) {
+	var total int
+	err := s.db.QueryRow(ctx, `SELECT COUNT(*) FROM transactions`).Scan(&total)
+	if err != nil {
+		return nil, 0, fmt.Errorf("service.ListTransactions: count: %w", err)
+	}
+
+	rows, err := s.db.Query(ctx, `
+		SELECT t.id,
+		       t.user_id,
+		       u.email,
+		       COALESCE(t.partner_id::text, ''),
+		       t.amount,
+		       t.type,
+		       COALESCE(t.description, ''),
+		       t.created_at
+		FROM transactions t
+		JOIN users u ON u.id = t.user_id
+		ORDER BY t.created_at DESC
+		LIMIT $1 OFFSET $2`,
+		limit, offset,
+	)
+	if err != nil {
+		return nil, 0, fmt.Errorf("service.ListTransactions: query: %w", err)
+	}
+	defer rows.Close()
+
+	var txs []AdminTransaction
+	for rows.Next() {
+		var t AdminTransaction
+		if err := rows.Scan(&t.ID, &t.UserID, &t.UserEmail, &t.PartnerID,
+			&t.Amount, &t.Type, &t.Description, &t.CreatedAt); err != nil {
+			return nil, 0, fmt.Errorf("service.ListTransactions: scan: %w", err)
+		}
+		txs = append(txs, t)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, 0, fmt.Errorf("service.ListTransactions: rows: %w", err)
+	}
+	return txs, total, nil
+}
+
+// ListStudents returns all users with role=student, ordered by name.
+func (s *Service) ListStudents(ctx context.Context) ([]Student, error) {
+	rows, err := s.db.Query(ctx,
+		`SELECT id, email, name, COALESCE(student_id, ''), balance
+		 FROM users
+		 WHERE role = 'student'
+		 ORDER BY name`,
+	)
+	if err != nil {
+		return nil, fmt.Errorf("service.ListStudents: %w", err)
+	}
+	defer rows.Close()
+
+	var students []Student
+	for rows.Next() {
+		var st Student
+		if err := rows.Scan(&st.ID, &st.Email, &st.Name, &st.StudentID, &st.Balance); err != nil {
+			return nil, fmt.Errorf("service.ListStudents: scan: %w", err)
+		}
+		students = append(students, st)
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("service.ListStudents: rows: %w", err)
+	}
+	return students, nil
+}
+
+// GetStats returns aggregated system statistics for the admin dashboard.
+func (s *Service) GetStats(ctx context.Context) (*Stats, error) {
+	var stats Stats
+
+	// Single query for all transaction aggregates.
+	err := s.db.QueryRow(ctx, `
+		SELECT
+			COALESCE(SUM(amount) FILTER (WHERE amount > 0), 0),
+			COALESCE(ABS(SUM(amount) FILTER (WHERE amount < 0)), 0)
+		FROM transactions`,
+	).Scan(&stats.TotalPointsIssued, &stats.TotalPointsSpent)
+	if err != nil {
+		return nil, fmt.Errorf("service.GetStats: transaction aggregates: %w", err)
+	}
+
+	err = s.db.QueryRow(ctx,
+		`SELECT COUNT(*) FROM users WHERE role = 'student'`,
+	).Scan(&stats.TotalStudents)
+	if err != nil {
+		return nil, fmt.Errorf("service.GetStats: total students: %w", err)
+	}
+
+	err = s.db.QueryRow(ctx,
+		`SELECT COUNT(*) FROM partners WHERE is_active = true`,
+	).Scan(&stats.ActivePartners)
+	if err != nil {
+		return nil, fmt.Errorf("service.GetStats: active partners: %w", err)
+	}
+
+	return &stats, nil
+}