Fix End Day not updating dashboard without refresh

Broadcast is_active in WS timer payload so the frontend can immediately
clear the session when the backend marks it complete.

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

frontend/src/stores/schedule.js

@@ -31,6 +31,11 @@ export const useScheduleStore = defineStore('schedule', () => {
       applySnapshot(event)
       return
     }
+    // Session ended
+    if (event.is_active === false) {
+      session.value = null
+      return
+    }
     // Timer events update session state
     if (event.current_block_id !== undefined && session.value) {
       session.value.current_block_id = event.current_block_id