feat(backend): implement user, ACL, and audit stacks

Add UserService (GetMe, UpdateMe, admin CRUD with block/unblock),
UserHandler (/users, /users/me), ACLHandler (GET/PUT /acl/:type/:id),
AuditHandler (GET /audit with all filters). Fix UserRepo.Update to
include is_blocked. Wire all remaining routes.

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

backend/internal/service/user_service.go

@@ -0,0 +1,156 @@
+package service
+
+import (
+	"context"
+	"fmt"
+
+	"golang.org/x/crypto/bcrypt"
+
+	"tanabata/backend/internal/domain"
+	"tanabata/backend/internal/port"
+)
+
+// UserService handles user CRUD and profile management.
+type UserService struct {
+	users port.UserRepo
+	audit *AuditService
+}
+
+// NewUserService creates a UserService.
+func NewUserService(users port.UserRepo, audit *AuditService) *UserService {
+	return &UserService{users: users, audit: audit}
+}
+
+// ---------------------------------------------------------------------------
+// Self-service
+// ---------------------------------------------------------------------------
+
+// GetMe returns the profile of the currently authenticated user.
+func (s *UserService) GetMe(ctx context.Context) (*domain.User, error) {
+	userID, _, _ := domain.UserFromContext(ctx)
+	return s.users.GetByID(ctx, userID)
+}
+
+// UpdateMeParams holds fields a user may change on their own profile.
+type UpdateMeParams struct {
+	Name     string  // empty = no change
+	Password *string // nil = no change
+}
+
+// UpdateMe allows a user to change their own name and/or password.
+func (s *UserService) UpdateMe(ctx context.Context, p UpdateMeParams) (*domain.User, error) {
+	userID, _, _ := domain.UserFromContext(ctx)
+
+	current, err := s.users.GetByID(ctx, userID)
+	if err != nil {
+		return nil, err
+	}
+
+	patch := *current
+	if p.Name != "" {
+		patch.Name = p.Name
+	}
+	if p.Password != nil {
+		hash, err := bcrypt.GenerateFromPassword([]byte(*p.Password), bcrypt.DefaultCost)
+		if err != nil {
+			return nil, fmt.Errorf("UserService.UpdateMe hash: %w", err)
+		}
+		patch.Password = string(hash)
+	}
+
+	return s.users.Update(ctx, userID, &patch)
+}
+
+// ---------------------------------------------------------------------------
+// Admin CRUD
+// ---------------------------------------------------------------------------
+
+// List returns a paginated list of users (admin only — caller must enforce).
+func (s *UserService) List(ctx context.Context, params port.OffsetParams) (*domain.UserPage, error) {
+	return s.users.List(ctx, params)
+}
+
+// Get returns a user by ID (admin only).
+func (s *UserService) Get(ctx context.Context, id int16) (*domain.User, error) {
+	return s.users.GetByID(ctx, id)
+}
+
+// CreateParams holds fields for creating a new user.
+type CreateUserParams struct {
+	Name      string
+	Password  string
+	IsAdmin   bool
+	CanCreate bool
+}
+
+// Create inserts a new user with a bcrypt-hashed password (admin only).
+func (s *UserService) Create(ctx context.Context, p CreateUserParams) (*domain.User, error) {
+	hash, err := bcrypt.GenerateFromPassword([]byte(p.Password), bcrypt.DefaultCost)
+	if err != nil {
+		return nil, fmt.Errorf("UserService.Create hash: %w", err)
+	}
+
+	u := &domain.User{
+		Name:      p.Name,
+		Password:  string(hash),
+		IsAdmin:   p.IsAdmin,
+		CanCreate: p.CanCreate,
+	}
+	created, err := s.users.Create(ctx, u)
+	if err != nil {
+		return nil, err
+	}
+
+	_ = s.audit.Log(ctx, "user_create", nil, nil, map[string]any{"target_user_id": created.ID})
+	return created, nil
+}
+
+// UpdateAdminParams holds fields an admin may change on any user.
+type UpdateAdminParams struct {
+	IsAdmin   *bool
+	CanCreate *bool
+	IsBlocked *bool
+}
+
+// UpdateAdmin applies an admin-level patch to a user.
+func (s *UserService) UpdateAdmin(ctx context.Context, id int16, p UpdateAdminParams) (*domain.User, error) {
+	current, err := s.users.GetByID(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+
+	patch := *current
+	if p.IsAdmin != nil {
+		patch.IsAdmin = *p.IsAdmin
+	}
+	if p.CanCreate != nil {
+		patch.CanCreate = *p.CanCreate
+	}
+	if p.IsBlocked != nil {
+		patch.IsBlocked = *p.IsBlocked
+	}
+
+	updated, err := s.users.Update(ctx, id, &patch)
+	if err != nil {
+		return nil, err
+	}
+
+	// Log block/unblock specifically.
+	if p.IsBlocked != nil {
+		action := "user_unblock"
+		if *p.IsBlocked {
+			action = "user_block"
+		}
+		_ = s.audit.Log(ctx, action, nil, nil, map[string]any{"target_user_id": id})
+	}
+	return updated, nil
+}
+
+// Delete removes a user by ID (admin only).
+func (s *UserService) Delete(ctx context.Context, id int16) error {
+	if err := s.users.Delete(ctx, id); err != nil {
+		return err
+	}
+	_ = s.audit.Log(ctx, "user_delete", nil, nil, map[string]any{"target_user_id": id})
+	return nil
+}