feat(core): consolidate auth service into backend and implement stripe billing

This commit performs a major architectural refactor by migrating the standalone `auth-service` into the main `backend` application, enabling a unified codebase and simplified deployment. It also introduces comprehensive Stripe billing support and a new administrative dashboard.

Key changes:
- **Architecture**: Deleted `apps/auth-service` and integrated its functionality (JWT, magic links, OAuth, user management) into `apps/backend`.
- **Billing**: Added Stripe integration to `backend`, supporting both monthly and yearly subscription cycles with automatic plan entitlement enforcement (e.g., location limits).
- **Admin Dashboard**: Implemented a new administrative service and API endpoints to manage tenants, users, and view platform-wide statistics.
- **Frontend**:
    - Added a new pricing page with monthly/yearly toggle and comparison table.
    - Integrated Stripe and Sentry for payments and error tracking.
    - Improved dashboard UX/UI and added i18n support for new features.
    - Enhanced the public booking flow with better validation and contact form integration.
- **Database**: Added migrations for users, magic links, password resets, OAuth states, admin audit logs, and refresh tokens.
- **DevOps**: Updated environment configurations for Railway and Vercel, and streamlined the project's `package.json` scripts.

apps/backend/internal/db/repository.go

@@ -38,6 +38,23 @@ type Repository interface {
 	UpdateTenantBillingState(ctx context.Context, tenantID string, planCode string, subscriptionStatus string, subscriptionID string) error
 	RecordBillingEvent(ctx context.Context, tenantID string, provider string, eventID string, eventType string, payload []byte) (bool, error)
 
+	// Auth methods
+	GetUserByEmail(ctx context.Context, email string) (*UserRecord, error)
+	GetUserByID(ctx context.Context, userID string) (*UserRecord, error)
+	CreateUser(ctx context.Context, email, passwordHash, name, provider, role string) (*UserRecord, error)
+	UpdateLastLogin(ctx context.Context, userID string) error
+	MarkEmailVerified(ctx context.Context, userID string) error
+	CreateMagicLink(ctx context.Context, token, userID, email string, expiresAt time.Time) error
+	GetMagicLink(ctx context.Context, token string) (*MagicLinkRecord, error)
+	MarkMagicLinkUsed(ctx context.Context, token string) error
+
+	// Admin methods
+	ListAllTenants(ctx context.Context, limit, offset int) ([]TenantRecord, int, error)
+	ListAllUsers(ctx context.Context, limit, offset int) ([]UserRecord, int, error)
+	GetPlatformStats(ctx context.Context) (PlatformStats, error)
+	CreateAdminAuditLog(ctx context.Context, params AdminAuditLogParams) error
+	UpdateUserRole(ctx context.Context, userID, role string) error
+
 	// Location / Zone Management
 	ListLocationsByTenant(ctx context.Context, tenantID string) ([]LocationRecord, error)
 	GetLocationByID(ctx context.Context, locationID string) (LocationRecord, error)
@@ -85,6 +102,46 @@ type TenantRecord struct {
 	BillingSubscription *string
 }
 
+type UserRecord struct {
+	ID            uuid.UUID
+	Email         string
+	Name          *string
+	PasswordHash  *string
+	EmailVerified bool
+	Provider      string
+	Role          string
+	CreatedAt     time.Time
+	LastLoginAt   *time.Time
+}
+
+type MagicLinkRecord struct {
+	Token     string
+	UserID    uuid.UUID
+	Email     string
+	Used      bool
+	ExpiresAt time.Time
+	CreatedAt time.Time
+}
+
+type PlatformStats struct {
+	TotalTenants       int64 `json:"totalTenants"`
+	TotalUsers         int64 `json:"totalUsers"`
+	ActiveSubscriptions int64 `json:"activeSubscriptions"`
+	TrialSubscriptions  int64 `json:"trialSubscriptions"`
+	BookingsThisMonth  int64 `json:"bookingsThisMonth"`
+	RevenueThisMonth   int64 `json:"revenueThisMonthCents"`
+}
+
+type AdminAuditLogParams struct {
+	AdminUserID  string
+	Action       string
+	ResourceType string
+	ResourceID   string
+	Details      map[string]any
+	IPAddress    string
+	UserAgent    string
+}
+
 type TenantMembershipRecord struct {
 	Tenant TenantRecord
 	UserID string
@@ -1303,6 +1360,60 @@ func (r *MemoryRepository) UpdateWorkingHours(_ context.Context, tenantID string
 	return pgx.ErrNoRows
 }
 
+// Auth methods for MemoryRepository
+func (r *MemoryRepository) GetUserByEmail(_ context.Context, email string) (*UserRecord, error) {
+	return nil, nil
+}
+
+func (r *MemoryRepository) GetUserByID(_ context.Context, userID string) (*UserRecord, error) {
+	return nil, nil
+}
+
+func (r *MemoryRepository) CreateUser(_ context.Context, email, passwordHash, name, provider, role string) (*UserRecord, error) {
+	return &UserRecord{ID: uuid.New(), Email: email, Name: &name, Provider: provider, Role: role}, nil
+}
+
+func (r *MemoryRepository) UpdateLastLogin(_ context.Context, userID string) error {
+	return nil
+}
+
+func (r *MemoryRepository) MarkEmailVerified(_ context.Context, userID string) error {
+	return nil
+}
+
+func (r *MemoryRepository) CreateMagicLink(_ context.Context, token, userID, email string, expiresAt time.Time) error {
+	return nil
+}
+
+func (r *MemoryRepository) GetMagicLink(_ context.Context, token string) (*MagicLinkRecord, error) {
+	return nil, nil
+}
+
+func (r *MemoryRepository) MarkMagicLinkUsed(_ context.Context, token string) error {
+	return nil
+}
+
+// Admin methods for MemoryRepository
+func (r *MemoryRepository) ListAllTenants(_ context.Context, limit, offset int) ([]TenantRecord, int, error) {
+	return []TenantRecord{r.tenant}, 1, nil
+}
+
+func (r *MemoryRepository) ListAllUsers(_ context.Context, limit, offset int) ([]UserRecord, int, error) {
+	return []UserRecord{}, 0, nil
+}
+
+func (r *MemoryRepository) GetPlatformStats(_ context.Context) (PlatformStats, error) {
+	return PlatformStats{TotalTenants: 1, TotalUsers: 1, ActiveSubscriptions: 1}, nil
+}
+
+func (r *MemoryRepository) CreateAdminAuditLog(_ context.Context, params AdminAuditLogParams) error {
+	return nil
+}
+
+func (r *MemoryRepository) UpdateUserRole(_ context.Context, userID, role string) error {
+	return nil
+}
+
 func Reference(prefix string, at time.Time) string {
 	return fmt.Sprintf("%s-%s-%s", prefix, at.UTC().Format("20060102150405"), strings.Split(uuid.NewString(), "-")[0])
 }