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.

packages/api-client/src/generated/types.ts

@@ -232,23 +232,57 @@ export interface components {
             primaryColor?: string;
             siteUrl?: string;
         };
+        /**
+         * @description Checkout launch response supporting both Stripe and Paddle providers.
+         *     For Stripe: checkoutUrl is returned (redirect-based checkout).
+         *     For Paddle: priceId, customerId, customerEmail, customData are returned (client-side checkout).
+         */
         CheckoutLaunchResponse: {
-            /** Format: uri */
-            cancelRedirectUrl: string;
-            customData: {
+            /**
+             * Format: uri
+             * @description URL to redirect after cancelled checkout
+             */
+            cancelRedirectUrl?: string;
+            /**
+             * Format: uri
+             * @description Stripe checkout URL (redirect the user to this URL)
+             */
+            checkoutUrl?: string;
+            /** @description Custom metadata for Paddle checkout */
+            customData?: {
                 [key: string]: string;
             };
-            /** Format: email */
+            /**
+             * Format: email
+             * @description Customer email for Paddle checkout
+             */
             customerEmail?: string;
+            /** @description Paddle customer ID */
             customerId?: string;
-            priceId: string;
-            /** Format: uri */
-            successRedirectUrl: string;
+            /** @description Paddle price ID for client-side checkout */
+            priceId?: string;
+            /**
+             * Format: uri
+             * @description URL to redirect after successful checkout
+             */
+            successRedirectUrl?: string;
         };
         CheckoutSessionRequest: {
-            /** @enum {string} */
+            /**
+             * @description Billing interval. Yearly gets 17% discount.
+             * @default monthly
+             * @enum {string}
+             */
+            billingInterval: "monthly" | "yearly";
+            /**
+             * @description Currency for the subscription
+             * @enum {string}
+             */
             currency?: "czk" | "usd";
-            /** @enum {string} */
+            /**
+             * @description The plan to subscribe to
+             * @enum {string}
+             */
             planCode: "starter" | "pro" | "business";
         };
         CreateBookingRequest: {
@@ -327,10 +361,20 @@ export interface components {
             timezone: string;
         };
         PlanDisplayPrice: {
+            /** @description Monthly price in cents */
             amountCents: number;
             /** @enum {string} */
             currency: "czk" | "usd";
+            /** @description Formatted monthly price string */
             formatted: string;
+            /** @description Yearly price in cents (17% discount) */
+            yearlyAmountCents?: number;
+            /** @description Formatted yearly price string */
+            yearlyFormatted?: string;
+            /** @description Description of yearly savings */
+            yearlySavings?: string;
+            /** @description Percentage saved with yearly billing */
+            yearlySavingsPercent?: number;
         };
         PlanEntitlements: {
             advancedReporting: boolean;