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/config/config.go

@@ -28,8 +28,14 @@ type Config struct {
 	PaddleAPIKey      string
 	PaddleWebhookKey  string
 	PaddlePriceMatrix map[string]map[string]string
+	StripeAPIKey      string
+	StripeWebhookKey  string
+	StripePriceMatrix map[string]map[string]string
+	AdminEmail        string
+	AdminKey          string
 	UmamiAPIURL       string
 	UmamiAPIKey       string
+	SentryDSN         string
 	DemoMode          bool
 }
 
@@ -53,8 +59,14 @@ func Load() (Config, error) {
 		PaddleAPIKey:      strings.TrimSpace(os.Getenv("BOOKRA_PADDLE_API_KEY")),
 		PaddleWebhookKey:  strings.TrimSpace(os.Getenv("BOOKRA_PADDLE_WEBHOOK_SECRET")),
 		PaddlePriceMatrix: paddlePriceMatrixFromEnv(),
+		StripeAPIKey:      strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_API_KEY")),
+		StripeWebhookKey:  strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_WEBHOOK_SECRET")),
+		StripePriceMatrix: stripePriceMatrixFromEnv(),
+		AdminEmail:        strings.TrimSpace(os.Getenv("BOOKRA_ADMIN_EMAIL")),
+		AdminKey:          strings.TrimSpace(os.Getenv("BOOKRA_ADMIN_KEY")),
 		UmamiAPIURL:       strings.TrimSpace(os.Getenv("BOOKRA_UMAMI_API_URL")),
 		UmamiAPIKey:       strings.TrimSpace(os.Getenv("BOOKRA_UMAMI_API_KEY")),
+		SentryDSN:         strings.TrimSpace(os.Getenv("BOOKRA_SENTRY_DSN")),
 		DemoMode:          boolFromEnv("BOOKRA_DEMO_MODE", false),
 	}
 
@@ -118,6 +130,34 @@ func (cfg Config) PaddleCheckoutConfigured(planCode string) bool {
 	return cfg.PaddleConfigured() && cfg.PaddleWebhookConfigured() && cfg.PaddlePriceMatrix[planCode]["czk"] != "" && cfg.PaddlePriceMatrix[planCode]["usd"] != ""
 }
 
+func (cfg Config) StripeConfigured() bool {
+	return strings.TrimSpace(cfg.StripeAPIKey) != ""
+}
+
+func (cfg Config) StripeWebhookConfigured() bool {
+	return strings.TrimSpace(cfg.StripeWebhookKey) != ""
+}
+
+func (cfg Config) StripeCheckoutConfigured(planCode string) bool {
+	planCode = shared.NormalizePlanCode(planCode)
+	return cfg.StripeConfigured() && cfg.StripeWebhookConfigured() && cfg.StripePriceMatrix[planCode]["czk"] != "" && cfg.StripePriceMatrix[planCode]["usd"] != ""
+}
+
+func (cfg Config) BillingProvider() string {
+	if cfg.StripeConfigured() {
+		return "stripe"
+	}
+	return "paddle"
+}
+
+func (cfg Config) BillingConfigured() bool {
+	return cfg.StripeConfigured() || cfg.PaddleConfigured()
+}
+
+func (cfg Config) BillingWebhookConfigured() bool {
+	return cfg.StripeWebhookConfigured() || cfg.PaddleWebhookConfigured()
+}
+
 func paddlePriceMatrixFromEnv() map[string]map[string]string {
 	matrix := map[string]map[string]string{
 		"starter":  {},
@@ -132,6 +172,32 @@ func paddlePriceMatrixFromEnv() map[string]map[string]string {
 	return matrix
 }
 
+func stripePriceMatrixFromEnv() map[string]map[string]string {
+	matrix := map[string]map[string]string{
+		"starter":  {},
+		"pro":      {},
+		"business": {},
+	}
+	for _, planCode := range []string{"starter", "pro", "business"} {
+		envPlan := strings.ToUpper(strings.ReplaceAll(planCode, "-", "_"))
+
+		// Monthly prices
+		matrix[planCode][planCode+":czk:monthly"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_CZK_MONTHLY_PRICE_ID"))
+		matrix[planCode][planCode+":usd:monthly"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_USD_MONTHLY_PRICE_ID"))
+		matrix[planCode][planCode+":czk"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_CZK_PRICE_ID"))
+		matrix[planCode][planCode+":usd"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_USD_PRICE_ID"))
+		matrix[planCode]["czk"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_CZK_PRICE_ID"))
+		matrix[planCode]["usd"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_USD_PRICE_ID"))
+
+		// Yearly prices
+		matrix[planCode][planCode+":czk:yearly"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_CZK_YEARLY_PRICE_ID"))
+		matrix[planCode][planCode+":usd:yearly"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_USD_YEARLY_PRICE_ID"))
+		matrix[planCode]["yearly:czk"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_CZK_YEARLY_PRICE_ID"))
+		matrix[planCode]["yearly:usd"] = strings.TrimSpace(os.Getenv("BOOKRA_STRIPE_" + envPlan + "_USD_YEARLY_PRICE_ID"))
+	}
+	return matrix
+}
+
 func normalizePaddleEnvironment(value string) string {
 	switch strings.ToLower(strings.TrimSpace(value)) {
 	case "live", "production":