Refactor role switcher: single item with arrows on right

- Remove separate "Кабинет" link and two role buttons
- Add single role switcher: "Я клиент <>" format
- Arrows <> shown only when user has both roles
- Click text → navigate to cabinet, click arrows → switch role

app/layouts/topnav.vue

@@ -17,8 +17,7 @@
         :theme="theme"
         :user-data="userData"
         :is-seller="isSeller"
-        :has-buyer-team="hasBuyerTeam"
-        :has-seller-team="hasSellerTeam"
+        :has-multiple-roles="hasMultipleRoles"
         :current-role="currentRole"
         :active-tokens="activeTokens"
         :available-chips="availableChips"
@@ -153,6 +152,7 @@ const sellerTeam = computed(() =>
 )
 const hasBuyerTeam = computed(() => !!buyerTeam.value)
 const hasSellerTeam = computed(() => !!sellerTeam.value)
+const hasMultipleRoles = computed(() => hasBuyerTeam.value && hasSellerTeam.value)
 const currentRole = computed(() =>
   userData.value?.activeTeam?.teamType || 'BUYER'
 )