Phase 6: fix the live Home Assistant write (Local Calendar, no event id)

The first live run against the new calendar.school entity failed loudly twice,
and both causes are fixed here.

- The Local Calendar rejects `return_response` on calendar.create_event. The
  client retries the call without it and ignores the changed-states array that
  Home Assistant returns instead.
- Home Assistant then reports no event id. The item keeps the description
  marker ([compass-nhs:<id>]) as its reference, so it leaves the candidate set
  and is never written twice. The live retry proved it: both events already in
  the calendar were adopted by their markers, with no duplicate.
- calendar.get_events reports `start` / `end` (a date-time or a bare date), not
  `start_date_time`; the reader now accepts all three shapes.

A model must no longer classify events. The calendar write depends on the
school-event rule, and the LLM labelled every event "normal"; events now keep
the deterministic rule under both classifiers.

Also fix the Phase 5 screenshot script: the calendar banner shares the `.scan`
class, so select each banner by its labelled section.

Docs record the accepted decision: Sam chose a Home Assistant Local Calendar,
so the target is calendar.school.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

internal/parse/importance.go

@@ -80,10 +80,17 @@ func eventIsSchoolEvent(title string) bool {
 // fails, loudly, on a model error or an unparseable answer; it never silently
 // leaves a wrong label. Items are updated in place. now lets the model judge
 // whether a due date is overdue.
+//
+// Calendar events keep the deterministic rule. A model must not decide whether
+// a class period is a "school event": the calendar write depends on that call
+// (FR-8), and a wrong label there either spams the family calendar with every
+// lesson or silently drops the notice they needed.
 func ClassifyModel(ctx context.Context, c Completer, items []Item, model string, now time.Time) error {
 	if c == nil {
 		return fmt.Errorf("classify: no model client configured")
 	}
+	ClassifyDeterministic(items, now)
+
 	const system = "You classify school items for a parent's morning brief. " +
 		"Reply with JSON only. No prose, no code fences."
 
@@ -107,6 +114,9 @@ func ClassifyModel(ctx context.Context, c Completer, items []Item, model string,
 			if i >= len(batch) {
 				return fmt.Errorf("classify: items %d-%d: model returned %d labels for %d items", start, end-1, len(labels), len(batch))
 			}
+			if batch[i].Type == TypeEvent {
+				continue // events keep the deterministic rule
+			}
 			switch label {
 			case importanceHigh, importanceNormal, importanceLow:
 				batch[i].Importance = label