security(auth): P1 Token Refresh + sessionStorage

- 新增三個 refresh 端點（member/provider/admin），revoke 舊 token 發行新 7 天 token
- axios.js / coachAxios.js：401 interceptor 改為 refresh-then-retry，含 isRefreshing queue 防並發、isRedirecting flag 防雙重 redirect
- auth.js / coachAuth.js / AuthCallbackView.vue：localStorage 全改為 sessionStorage
- echo.js / notificationAxios.js：同步改為 sessionStorage
- notifications.js：401 時停止 polling（stopPolling），不印 error log
- 新增 TokenRefreshTest.php（11 tests / 24 assertions）：refresh 成功/失效/跨角色 403

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/stores/notifications.js

@@ -25,6 +25,7 @@ export const useNotificationStore = defineStore('notifications', () => {
         }
       }
     } catch (e) {
+      if (e?.response?.status === 401) { stopPolling(); return }
       console.error('[NotificationStore] fetchUnreadCount failed:', e?.response?.status, e?.message)
     }
   }
@@ -35,6 +36,7 @@ export const useNotificationStore = defineStore('notifications', () => {
       notifications.value = res.data.data
       unreadCount.value   = res.data.unread_count
     } catch (e) {
+      if (e?.response?.status === 401) { stopPolling(); return }
       console.error('[NotificationStore] fetchNotifications failed:', e?.response?.status, e?.message)
     }
   }