feat(api): implement centralized API client and refactor vendor pages

Introduced a new API client in src/lib/api/ to handle requests securely. Refactored vendor pages to use this client. Updated authentication logic in layout and login pages.

src/routes/(app)/login/+page.svelte

@@ -1,7 +1,8 @@
 <script lang="ts">
   import { goto } from '$app/navigation';
   import { user } from '$lib/states';
-  import type { LoginRequest } from '$lib/types/types';
+  import { api } from '$lib/api';
+  import type { LoginRequest } from '$lib/api';
 
   let username = '';
   let password = '';
@@ -17,39 +18,18 @@
     isLoading = true;
     errorMessage = '';
 
-    try {
-      const response = await fetch('http://localhost:9552/auth/login', {
-        method: 'POST',
-        headers: {
-          'Content-Type': 'application/json'
-        },
-        body: JSON.stringify(loginData)
-      });
+    const result = await api.auth.login(loginData);
 
-      if (!response.ok) {
-        const errorData = await response.json();
-        errorMessage = errorData.error || 'Login failed';
-      } else {
-        const data = await response.json();
-        // Assuming the backend returns a token or some success indicator
-        // Store the token in localStorage for authentication checks
-        if (data.token) {
-          localStorage.setItem('auth_token', data.token);
-        }
-        // Store the user object in localStorage
-        localStorage.setItem('user', JSON.stringify(data.user));
-
-        // Update the user store
-        user.set(data.user);
-
-        // Redirect to vendor page after successful login
-        goto('/vendor');
-      }
-    } catch (err) {
-      errorMessage = 'An error occurred. Please try again.';
-    } finally {
-      isLoading = false;
+    if (result.error) {
+      errorMessage = result.error;
+    } else if (result.data) {
+      // Update the user store
+      user.set(result.data.user);
+      // Redirect to vendor page after successful login
+      goto('/vendor');
     }
+
+    isLoading = false;
   }
 </script>