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/parse/importance.go

@@ -7,6 +7,8 @@ import (
 	"sort"
 	"strings"
 	"time"
+
+	"gitea.lab.audasmedia.com.au/sam/compass_teams_nhs/internal/period"
 )
 
 // Importance labels stored in items.importance (FR-4).
@@ -69,11 +71,11 @@ func deterministicImportance(it Item, week time.Time) string {
 // "End of Year Senior Music Concert - HALL (...) - KSH, CFR". The first part of
 // a lesson is a period label ("5", "C" or "RLE GROUP D").
 func eventIsSchoolEvent(title string) bool {
-	parts := splitDash(title)
+	parts := period.SplitDash(title)
 	if len(parts) == 0 || strings.TrimSpace(parts[0]) == "" {
 		return false
 	}
-	return !periodLabel.MatchString(parts[0])
+	return !period.IsPeriodLabel(parts[0])
 }
 
 // ClassifyModel asks a model to classify importance for every item (FR-4). It