Document the HA-side webhook automation

The calendar-sync feature landed 2026-09-02 but only the app.py half —
the HA automation to receive the webhook and create the calendar event
was never built, so it silently did nothing. Built it now
(automation.lunch_menu_family_calendar: local_only webhook trigger ->
calendar.create_event on calendar.family) and documented where to look
on each side when this breaks again.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KsJqAZ82Veyf5oihBr71S5

CLAUDE.md

@@ -20,12 +20,21 @@ Runs as one Docker container on the user's Unraid home server.
   first time, before a settings file exists.
 - Vacation ranges suppress sends without disabling the schedule — checked
   fresh on every run via `is_on_vacation()`.
-- **Home Assistant integration (2026-09-02):** if `HA_WEBHOOK_URL` is set,
+- **Home Assistant integration (2026-09-02, HA side built 2026-09-03):** if
-  every successful menu fetch also POSTs `{"date": ..., "items": [...]}` to
+  `HA_WEBHOOK_URL` is set, every successful menu fetch also POSTs
-  that webhook, independent of whether the SMS send itself succeeds. An HA
+  `{"date": ..., "items": [...]}` to that webhook, independent of whether
-  automation (webhook trigger → `calendar.create_event`) turns this into an
+  the SMS send itself succeeds. On the HA side (`automation.lunch_menu_family_calendar`,
-  all-day calendar event with the menu. This makes the scrape here the
+  `http://192.168.86.207:8123`), a `local_only` webhook trigger runs
-  single source of truth — HA doesn't poll or re-scrape anything.
+  `calendar.create_event` against `calendar.family`, producing an all-day
+  event with the menu as the description (bulleted). This makes the
+  scrape here the single source of truth — HA doesn't poll or re-scrape
+  anything. The webhook id is a random token that lives only in the
+  server's `.env` (`HA_WEBHOOK_URL`) and in the automation's trigger
+  config — never committed here. If the calendar push stops working,
+  check both ends: `GET /api/integrations` on this app reports whether
+  `HA_WEBHOOK_URL` is set at all, and `ha_get_automation_traces` on
+  `automation.lunch_menu_family_calendar` shows whether HA is even
+  receiving the webhook.
 - **Manual actions (2026-09-03):** besides "Send Lunch Menu Now" (full job —
   scrape, HA push, text everyone), the UI has "Push to Calendar Only"
   (`POST /api/push-calendar` → `push_calendar_only()`, scrape + HA push, no