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>

docs/phase-6-calendar-notes.md

@@ -1,5 +1,11 @@
 # Phase 6 — the calendar write (Sam's Home Assistant calendar)
 
+> **Updated by Phase 6b (AUD-119):** the calendar now holds each child's
+> **periods**, **work due**, **work overdue** and the **major school events**,
+> per child, on every pass. See
+> [`phase-6b7b-notes.md`](phase-6b7b-notes.md). The Phase 6 mechanism below
+> (Local Calendar, marker idempotency, fail loud) is unchanged.
+
 Status: **done** (AUD-110). Sam chose a **Home Assistant Local Calendar**, and
 the service writes important school events to it through the Home Assistant REST
 API.