feat: Add comprehensive backend validation, toast notifications, and Tokyo Night theme

- Backend: Add server-side validation with go-playground/validator/v10
- Frontend: Add toast notifications for API errors with @zerodevx/svelte-toast
- UI: Complete Tokyo Night theme redesign with modern animations
- Docs: Update COMPLETE_DOCUMENTATION.md and README.md with all enhancements
- Validation: Email format, password strength, and input sanitization
- UX: Real-time error feedback, loading states, and responsive design

bruno/README.md

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+# Bruno API Tests for Ebook Reader
+
+This directory contains Bruno collection for testing the Ebook Reader API with comprehensive REST documentation.
+
+## Setup
+
+1. Install Bruno: https://www.usebruno.com/
+2. Open Bruno and import this collection folder
+3. Select the "localhost" environment
+4. Start the application with `docker-compose up --build`
+5. Register/Login first, then use Bearer token for protected endpoints
+
+## Available Tests
+
+### Auth (Public Endpoints)
+- **Register User**: POST /api/auth/register - Create new account
+- **Login User**: POST /api/auth/login - Authenticate (email or username)
+- **Get Profile**: GET /api/auth/profile - Get user info (requires token)
+
+### Ebooks (Protected - JWT Required)
+- **List Ebooks**: GET /api/ebooks - Paginated ebook list
+- **Get Ebook**: GET /api/ebooks/:id - Single ebook details
+- **Create Ebook**: POST /api/ebooks - Add new ebook
+- **Update Ebook**: PUT /api/ebooks/:id - Modify ebook metadata
+- **Delete Ebook**: DELETE /api/ebooks/:id - Remove ebook
+
+### Reading Progress (Protected - JWT Required)
+- **Get Reading Progress**: GET /api/ebooks/:id/progress - User's progress
+- **Update Reading Progress**: PUT /api/ebooks/:id/progress - Update progress
+
+## Documentation Features
+
+Each request includes:
+- **Detailed descriptions** of functionality
+- **Parameter specifications** (required/optional, types)
+- **Request/Response examples**
+- **Error response codes** and meanings
+- **Authentication requirements**
+
+## Notes
+
+- **Authentication Flow**: Register → Login → Use Bearer token for all other requests
+- **JWT Tokens**: Valid for 24 hours, include in `Authorization: Bearer <token>` header
+- **User Isolation**: Progress and data are user-specific
+- **Variables**: Update `ebook_id` for testing specific ebooks
+- **Security**: Passwords hashed with bcrypt, unique email/username constraints
+- **JSON**: All requests/responses use JSON format