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/catalog/service.go

@@ -3,6 +3,7 @@ package catalog
 import (
 	"context"
 	"errors"
+	"fmt"
 	"time"
 
 	"bookra/apps/backend/internal/db"
@@ -17,14 +18,25 @@ var (
 	ErrInvalidBooking     = errors.New("invalid booking request")
 	ErrTenantNotFound     = errors.New("tenant not found")
 	ErrTenantMembership   = errors.New("tenant membership not found")
+	ErrPlanLimitReached   = errors.New("plan limit reached")
 )
 
 type Service struct {
-	repo db.Repository
+	repo           db.Repository
+	billingService interface {
+		GetEntitlements(ctx context.Context, tenantID string) (domain.PlanEntitlements, error)
+	}
+	notificationService interface {
+		SendUsageWarning(ctx context.Context, tenantID string, locationCount, locationLimit, usagePercent int) error
+	}
 }
 
-func NewService(repo db.Repository) *Service {
-	return &Service{repo: repo}
+func NewService(repo db.Repository, billingService interface {
+	GetEntitlements(ctx context.Context, tenantID string) (domain.PlanEntitlements, error)
+}, notificationService interface {
+	SendUsageWarning(ctx context.Context, tenantID string, locationCount, locationLimit, usagePercent int) error
+}) *Service {
+	return &Service{repo: repo, billingService: billingService, notificationService: notificationService}
 }
 
 // ============================================
@@ -63,6 +75,18 @@ func (s *Service) CreateLocation(ctx context.Context, principal domain.Principal
 		return domain.Location{}, ErrTenantMembership
 	}
 
+	// Check plan entitlements for location limit
+	if s.billingService != nil {
+		entitlements, err := s.billingService.GetEntitlements(ctx, membership.Tenant.ID)
+		if err == nil && entitlements.MaxLocations > 0 {
+			// Count existing locations
+			locations, err := s.repo.ListLocationsByTenant(ctx, membership.Tenant.ID)
+			if err == nil && len(locations) >= entitlements.MaxLocations {
+				return domain.Location{}, fmt.Errorf("%w: location limit reached (%d/%d). Upgrade your plan to add more locations.", ErrPlanLimitReached, len(locations), entitlements.MaxLocations)
+			}
+		}
+	}
+
 	params := db.CreateLocationParams{
 		TenantID: membership.Tenant.ID,
 		Name:     req.Name,
@@ -74,6 +98,18 @@ func (s *Service) CreateLocation(ctx context.Context, principal domain.Principal
 		return domain.Location{}, err
 	}
 
+	// Send usage warning if at 80%+ of limit
+	if s.notificationService != nil && s.billingService != nil {
+		entitlements, err := s.billingService.GetEntitlements(ctx, membership.Tenant.ID)
+		if err == nil && entitlements.MaxLocations > 0 {
+			locations, _ := s.repo.ListLocationsByTenant(ctx, membership.Tenant.ID)
+			usagePercent := (len(locations) * 100) / entitlements.MaxLocations
+			if usagePercent >= 80 {
+				_ = s.notificationService.SendUsageWarning(ctx, membership.Tenant.ID, len(locations), entitlements.MaxLocations, usagePercent)
+			}
+		}
+	}
+
 	return domain.Location{
 		ID:        rec.ID,
 		TenantID:  rec.TenantID,