fix: prevent unwanted login redirects during WebSocket reconnection (#6410)

## 🐛 Problem

Users were experiencing the following issues during WebSocket
reconnection:

1. Automatic redirect to login page after "Reconnecting" toast message
appears
2. Automatic re-login after a few seconds, returning to the main
interface
3. This cycle repeats, severely degrading user experience

## 🔍 Root Cause Analysis

### 1. Router Guard Catching Too Many Errors
```typescript
// Problematic code
try {
  const { getUserCloudStatus, getSurveyCompletedStatus } = await import('@/api/auth')
  const userStatus = await getUserCloudStatus()
  // ...
} catch (error) {
  // All types of errors are caught here
  return next({ name: 'cloud-user-check' })
}
```

With dynamic import inside the try block, the following were all being
caught:
- Errors during `@/api/auth` module loading
- Runtime errors from the API singleton
- Actual API call errors

Everything was caught and redirected to `cloud-user-check`.

### 2. Full Page Reload in UserCheckView
```typescript
// Problematic code
window.location.href = '/'  // Full page reload!
```

This caused:
- Loss of SPA benefits
- Firebase Auth re-initialization → temporarily null user
- Router guard re-execution → potential for another redirect

## ✅ Solution

### 1. router.ts: Move dynamic import outside try block
```typescript
// After fix
const { getUserCloudStatus, getSurveyCompletedStatus } = await import('@/api/auth')

try {
  // Only API calls inside try
  const userStatus = await getUserCloudStatus()
  // ...
} catch (error) {
  // Now only catches pure API call errors
  return next({ name: 'cloud-user-check' })
}
```

### 2. UserCheckView.vue: Use SPA routing
```typescript
// After fix
await router.replace('/')  // Use Vue Router instead of window.location.href
```

🤖 Generated with [Claude Code](https://claude.ai/code)

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6410-fix-prevent-unwanted-login-redirects-during-WebSocket-reconnection-29c6d73d3650818a8a1acbdcebd2f703)
by [Unito](https://www.unito.io)

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: GitHub Action <action@github.com>

src/platform/cloud/subscription/composables/useSubscription.ts

@@ -1,5 +1,5 @@
-import { computed, ref, watch } from 'vue'
 import { createSharedComposable } from '@vueuse/core'
+import { computed, ref, watch } from 'vue'
 
 import { useCurrentUser } from '@/composables/auth/useCurrentUser'
 import { useFirebaseAuthActions } from '@/composables/auth/useFirebaseAuthActions'

src/platform/onboarding/cloud/UserCheckView.vue

@@ -74,7 +74,7 @@ const {
     }
 
     // User is fully onboarded
-    window.location.href = '/'
+    await router.replace('/')
   }),
   null,
   { resetOnExecute: false }