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

frontend/src/lib/api.ts

@@ -0,0 +1,170 @@
+import { showError } from './toast';
+
+const API_BASE = import.meta.env.DEV ? 'http://localhost:8080/api' : '/api';
+
+// Helper function to handle API responses and show error toasts
+async function handleResponse<T>(response: Response, errorMessage: string): Promise<T> {
+	if (!response.ok) {
+		let message = errorMessage;
+		try {
+			const errorData = await response.json();
+			if (errorData.error) {
+				message = errorData.error;
+			}
+		} catch (e) {
+			// If we can't parse JSON, use the default message
+		}
+		showError(message);
+		throw new Error(message);
+	}
+	return response.json();
+}
+
+export interface User {
+  id: string;
+  email: string;
+  username: string;
+}
+
+export interface AuthResponse {
+  token: string;
+  user: User;
+}
+
+export interface Ebook {
+  id: string;
+  title: string;
+  author: string | null;
+  isbn: string | null;
+  description: string | null;
+  file_path: string;
+  file_size: number | null;
+  mime_type: string | null;
+  cover_image_path: string | null;
+  created_at: string;
+  updated_at: string;
+}
+
+export interface ReadingProgress {
+  ebook_id: string;
+  user_id: string;
+  current_page: number;
+  total_pages: number | null;
+  last_read_at: string;
+}
+
+// Get stored token
+function getToken(): string | null {
+  if (typeof window !== 'undefined') {
+    return localStorage.getItem('auth_token');
+  }
+  return null;
+}
+
+// Create headers with auth
+function createHeaders(): Record<string, string> {
+  const headers: Record<string, string> = {
+    'Content-Type': 'application/json',
+  };
+
+  const token = getToken();
+  if (token) {
+    headers['Authorization'] = `Bearer ${token}`;
+  }
+
+  return headers;
+}
+
+// Auth functions
+export async function registerUser(email: string, username: string, password: string): Promise<AuthResponse> {
+  const response = await fetch(`${API_BASE}/auth/register`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ email, username, password }),
+  });
+  return handleResponse<AuthResponse>(response, 'Registration failed');
+}
+
+export async function loginUser(login: string, password: string): Promise<AuthResponse> {
+  const response = await fetch(`${API_BASE}/auth/login`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify({ login, password }),
+  });
+  return handleResponse<AuthResponse>(response, 'Login failed');
+}
+
+export async function getUserProfile(): Promise<User> {
+  const response = await fetch(`${API_BASE}/auth/profile`, {
+    headers: createHeaders(),
+  });
+  return handleResponse<User>(response, 'Failed to get profile');
+}
+
+export async function fetchEbooks(limit: number = 20, offset: number = 0): Promise<Ebook[]> {
+  const response = await fetch(`${API_BASE}/ebooks?limit=${limit}&offset=${offset}`, {
+    headers: createHeaders(),
+  });
+  return handleResponse<Ebook[]>(response, 'Failed to fetch ebooks');
+}
+
+export async function fetchEbook(id: string): Promise<Ebook> {
+  const response = await fetch(`${API_BASE}/ebooks/${id}`, {
+    headers: createHeaders(),
+  });
+  return handleResponse<Ebook>(response, 'Failed to fetch ebook');
+}
+
+export async function createEbook(data: Partial<Ebook>): Promise<Ebook> {
+  const response = await fetch(`${API_BASE}/ebooks`, {
+    method: 'POST',
+    headers: createHeaders(),
+    body: JSON.stringify(data),
+  });
+  return handleResponse<Ebook>(response, 'Failed to create ebook');
+}
+
+export async function updateEbook(id: string, data: Partial<Ebook>): Promise<Ebook> {
+  const response = await fetch(`${API_BASE}/ebooks/${id}`, {
+    method: 'PUT',
+    headers: createHeaders(),
+    body: JSON.stringify(data),
+  });
+  return handleResponse<Ebook>(response, 'Failed to update ebook');
+}
+
+export async function deleteEbook(id: string): Promise<void> {
+  const response = await fetch(`${API_BASE}/ebooks/${id}`, {
+    method: 'DELETE',
+    headers: createHeaders(),
+  });
+  if (!response.ok) {
+    let message = 'Failed to delete ebook';
+    try {
+      const errorData = await response.json();
+      if (errorData.error) {
+        message = errorData.error;
+      }
+    } catch (e) {
+      // If we can't parse JSON, use the default message
+    }
+    showError(message);
+    throw new Error(message);
+  }
+}
+
+export async function fetchReadingProgress(ebookId: string): Promise<ReadingProgress> {
+  const response = await fetch(`${API_BASE}/ebooks/${ebookId}/progress`, {
+    headers: createHeaders(),
+  });
+  return handleResponse<ReadingProgress>(response, 'Failed to fetch reading progress');
+}
+
+export async function updateReadingProgress(ebookId: string, currentPage: number, totalPages?: number): Promise<ReadingProgress> {
+  const response = await fetch(`${API_BASE}/ebooks/${ebookId}/progress`, {
+    method: 'PUT',
+    headers: createHeaders(),
+    body: JSON.stringify({ current_page: currentPage, total_pages: totalPages }),
+  });
+  return handleResponse<ReadingProgress>(response, 'Failed to update reading progress');
+}