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.

README.md

@@ -58,3 +58,46 @@ npm run db:migrate:up
 ```
 
 `db:migrate:*` expects `BOOKRA_DATABASE_DIRECT_URL` to be exported in the shell.
+
+## Brand Colors
+
+Bookra uses a sophisticated color system designed for modern booking interfaces with support for both light and dark themes.
+
+### Primary Palette
+- **Canvas** (`--color-canvas`): #FFFFFF (light) / #0A0A0A (dark)
+- **Canvas Elevated** (`--color-canvas-elevated`): #F8F9FA (light) / #1A1A1A (dark)
+- **Canvas Sunken** (`--color-canvas-sunken`): #F1F3F4 (light) / #252525 (dark)
+
+### Accent Colors
+- **Primary** (`--color-primary`): #3B82F6
+- **Primary Hover** (`--color-primary-hover`): #2563EB
+- **Primary Active** (`--color-primary-active`): #1D4ED8
+
+### Semantic Colors
+- **Success** (`--color-success`): #10B981
+- **Warning** (`--color-warning`): #F59E0B
+- **Error** (`--color-error`): #EF4444
+- **Info** (`--color-info`): #06B6D4
+
+### Text Colors
+- **Text Primary** (`--color-text-primary`): #111827 (light) / #F9FAFB (dark)
+- **Text Secondary** (`--color-text-secondary`): #6B7280 (light) / #D1D5DB (dark)
+- **Text Muted** (`--color-text-muted`): #9CA3AF (light) / #9CA3AF (dark)
+
+### Border & Surface
+- **Border** (`--color-border`): #E5E7EB (light) / #374151 (dark)
+- **Surface Glass** (`--color-surface-glass`): rgba(255, 255, 255, 0.8) (light) / rgba(0, 0, 0, 0.8) (dark)
+
+### Shadow System
+- **Shadow XS** (`--shadow-xs`): 0 1px 2px 0 rgba(0, 0, 0, 0.05)
+- **Shadow SM** (`--shadow-sm`): 0 1px 3px 0 rgba(0, 0, 0, 0.1), 0 1px 2px 0 rgba(0, 0, 0, 0.06)
+- **Shadow MD** (`--shadow-md`): 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06)
+- **Shadow LG** (`--shadow-lg`): 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05)
+- **Shadow XL** (`--shadow-xl`): 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04)
+- **Shadow 2XL** (`--shadow-2xl`): 0 25px 50px -12px rgba(0, 0, 0, 0.25)
+
+### Animation Timing
+- **Ease Out Expo** (`--ease-out-expo`): cubic-bezier(0.16, 1, 0.3, 1)
+- **Ease Spring** (`--ease-spring`): cubic-bezier(0.68, -0.55, 0.265, 1.55)
+
+These colors are implemented as CSS custom properties and are used throughout the frontend application for consistent theming and accessibility.