Refactor login error handling and improve user feedback

- Update LoginForm component to display error messages directly from the authentication response.
- Modify useAuth composable to handle login errors more effectively, ensuring proper error messages are thrown.
- Enhance login API response to return structured error messages for invalid credentials.
- Adjust Cidaas utility to throw specific errors for invalid username/password scenarios.

.claude/settings.local.json

@@ -49,7 +49,8 @@
       "WebFetch(domain:www.shadcn-vue.com)",
       "WebFetch(domain:docs.cidaas.com)",
       "WebFetch(domain:articles.cidaas.de)",
-      "WebFetch(domain:pre-release-docs.cidaas.com)"
+      "WebFetch(domain:pre-release-docs.cidaas.com)",
+      "mcp__playwright__browser_console_messages"
     ],
     "deny": [],
     "ask": []