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/frontend/package.json

@@ -14,7 +14,9 @@
     "@bookra/shared-types": "0.1.0",
     "@neondatabase/neon-js": "^0.2.0-beta.1",
     "@paddle/paddle-js": "^1.3.2",
+    "@sentry/react": "^10.52.0",
     "@solidjs/router": "^0.15.3",
+    "@stripe/stripe-js": "^4.0.0",
     "solid-js": "^1.9.5"
   },
   "devDependencies": {