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/cmd/api/main.go

@@ -11,14 +11,37 @@ import (
 	"bookra/apps/backend/internal/api"
 	"bookra/apps/backend/internal/config"
 	"bookra/apps/backend/internal/db"
+
+	sentry "github.com/getsentry/sentry-go"
 )
 
+func initSentry(cfg config.Config) {
+	if cfg.SentryDSN == "" {
+		log.Println("Sentry DSN not configured - skipping initialization")
+		return
+	}
+
+	err := sentry.Init(sentry.ClientOptions{
+		Dsn:         cfg.SentryDSN,
+		Environment: cfg.Environment,
+		Release:     "bookra@1.0.0",
+		// Set TracesSampleRate to 1.0 to capture 100% of transactions for testing
+		TracesSampleRate: 1.0,
+	})
+	if err != nil {
+		log.Fatalf("Sentry initialization failed: %v", err)
+	}
+	log.Println("Sentry initialized")
+}
+
 func main() {
 	cfg, err := config.Load()
 	if err != nil {
 		log.Fatalf("load config: %v", err)
 	}
 
+	initSentry(cfg)
+
 	pools, err := db.NewPools(cfg)
 	if err != nil {
 		log.Fatalf("create database pools: %v", err)
@@ -31,6 +54,9 @@ func main() {
 	}
 	defer server.Close()
 
+	// Start background job for trial ending emails
+	go server.StartBackgroundJobs()
+
 	httpServer := &http.Server{
 		Addr:              ":" + cfg.Port,
 		Handler:           server.Handler(),