Phase 6b/7b: per-child decoded periods, separate brief blocks, idempotent calendar (AUD-119)

- Parse each child's own "Today" day widget for the timetable (FR-16); drop the
  school-wide week calendar's lesson grid and clean the leaked routine rows.
- Add the editable codes map (FR-17): subjects, rooms, teachers and period
  labels, seeded, an unknown code falls back to the raw code; `school codes` CLI.
- Brief: Finn's block first, then Harry's, four sections always present (FR-9);
  periods decoded into plain English; the undated tail is one counted line (FR-18).
- Calendar: write periods + work due + work overdue + major events, per child,
  on every pass. Identity is the stable per-item key, so a re-run never re-inserts
  (FR-8). morning-brief.sh now runs scan -> calendar push -> notify.
- Day-widget labels are 12-hour: 1-6 read as PM, fixing afternoon periods.

Proven live on .13: image 0.6.2-phase6b7b; both children's briefs decoded and
separate; 35 events in calendar.school; runs 2 and 3 of the scan added nothing.

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

internal/store/store.go

@@ -375,6 +375,40 @@ func (s *Store) DeleteChildCompassTasksFromPages(ctx context.Context, childID in
 	return res.RowsAffected()
 }
 
+// DeleteItemsFromPages is DeleteItems narrowed to the given source pages. It is
+// used to drop a stale snapshot (for example a child's previously parsed day
+// widget) without touching the same child's other rows.
+func (s *Store) DeleteItemsFromPages(ctx context.Context, childID int64, source, itemType string, pages ...string) (int64, error) {
+	if len(pages) == 0 {
+		return 0, nil
+	}
+	placeholders := strings.Repeat("?, ", len(pages))
+	placeholders = strings.TrimSuffix(placeholders, ", ")
+	q := `DELETE FROM items WHERE child_id = ?`
+	args := []any{childID}
+	if source != "" {
+		q += ` AND source = ?`
+		args = append(args, source)
+	}
+	if itemType != "" {
+		q += ` AND type = ?`
+		args = append(args, itemType)
+	}
+	q += ` AND source_page IN (` + placeholders + `)`
+	for _, p := range pages {
+		args = append(args, p)
+	}
+	res, err := s.db.ExecContext(ctx, q, args...)
+	if err != nil {
+		return 0, fmt.Errorf("delete items for child %d from pages: %w", childID, err)
+	}
+	n, err := res.RowsAffected()
+	if err != nil {
+		return 0, err
+	}
+	return n, nil
+}
+
 // TypeCount is the number of items of one type for one child.
 type TypeCount struct {
 	Child string