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/decode/decode_test.go

@@ -0,0 +1,52 @@
+package decode
+
+import (
+	"testing"
+
+	"gitea.lab.audasmedia.com.au/sam/compass_teams_nhs/internal/store"
+)
+
+func testCodes() store.CodeMap {
+	return store.CodeMap{
+		Subject: map[string]string{"7SCF": "Year 7 Science", "11MGMAC2": "Year 11 General Maths"},
+		Room:    map[string]string{"H14LAB": "Room H14LAB", "B11": "Room B11"},
+		Teacher: map[string]string{"KNI": "Mr KNI", "GT": "Mr GT"},
+		Period:  map[string]string{"C": "Connect"},
+	}
+}
+
+// TestPeriodDecodesKnownCodes proves FR-17: a lesson reads as plain English.
+func TestPeriodDecodesKnownCodes(t *testing.T) {
+	cases := map[string]string{
+		"1 - 7SCF - H14LAB - KNI": "Period 1 — Year 7 Science — Room H14LAB — Mr KNI",
+		"3 - 11MGMAC2 - B11 - GT": "Period 3 — Year 11 General Maths — Room B11 — Mr GT",
+		"C - 11MGMAC2 - B11 - GT": "Connect — Year 11 General Maths — Room B11 — Mr GT",
+		"RLE GROUP D - IM1 - RLE": "RLE GROUP D — IM1 — RLE",
+		"5 - 11HLEGB5 - D8":       "Period 5 — 11HLEGB5 — D8",
+		"2 - 11HLEGB5":            "Period 2 — 11HLEGB5",
+	}
+	for raw, want := range cases {
+		if got := Period(raw, testCodes()); got != want {
+			t.Errorf("Period(%q) = %q, want %q", raw, got, want)
+		}
+	}
+}
+
+// TestPeriodUnknownCodesRenderRaw proves the fallback: a code that is not in
+// the editable map renders as the raw code, never blank (FR-17).
+func TestPeriodUnknownCodesRenderRaw(t *testing.T) {
+	got := Period("1 - 7ZZZ - Z99 - ZZZ", testCodes())
+	want := "Period 1 — 7ZZZ — Z99 — ZZZ"
+	if got != want {
+		t.Errorf("Period = %q, want %q", got, want)
+	}
+}
+
+// TestPeriodLeavesEventsAlone proves a school event is not mangled by the
+// lesson decoder.
+func TestPeriodLeavesEventsAlone(t *testing.T) {
+	raw := "End of Year Senior Music Concert - HALL - KSH, CFR"
+	if got := Period(raw, testCodes()); got != raw {
+		t.Errorf("Period = %q, want the event unchanged", got)
+	}
+}