feat(auth): enhance login flow with notifications and path normalization

- add success notification on successful login
- show error notification with detailed message on login failure
- normalize API paths to prevent double slashes and trailing slashes
- redirect to login page only if not on login request or page

web/src/pages/LoginPage.tsx

@@ -13,6 +13,7 @@ import {
   Center,
   Box
 } from '@mantine/core';
+import { notifications } from '@mantine/notifications';
 import { IconAlertCircle, IconBrandWhatsapp } from '@tabler/icons-react';
 import { useAuthStore } from '../stores/authStore';
 
@@ -28,10 +29,24 @@ export default function LoginPage() {
 
     try {
       await login(username, password);
+      notifications.show({
+        title: 'Login successful',
+        message: 'Welcome back!',
+        color: 'green',
+      });
       navigate('/');
-    } catch (err) {
-      // Error is handled in the store
-      console.error('Login failed:', err);
+    } catch (err: any) {
+      const responseData = err?.response?.data;
+      const notificationMessage =
+        responseData?.message ||
+        (typeof responseData === 'string' ? responseData.trim() : '') ||
+        'Invalid username or password';
+
+      notifications.show({
+        title: 'Login failed',
+        message: notificationMessage,
+        color: 'red',
+      });
     }
   };