Phase 9d: Notification cron + multilingual templates + status badges

Backend (school-service):
  - notification_log table with UNIQUE(event_id, lead_days, audience,
    channel) for idempotent re-runs. Status enum sent/failed/skipped.
  - internal/notifications/templates.go: per-event-type × audience ×
    lead-day-bucket × language templates in 8 languages (de/en/tr/ar/
    uk/ru/pl/fr). Fallback chain (lang→de, eventType→andere) so we
    never miss a render.
  - service.go scans cal_school_event for events whose
    (start_date - runDate) appears in notification_lead_days. For each
    due (audience, channel) tuple it dispatches via POST to the
    Matrix/Email upstreams owned by the colleague's services.
    Empty URL → status='skipped', logged for visibility.
  - dispatcher.go handles the POST, parent-recipient lookup (joins
    parent_account + parent_child + cal_school_event.affected_class_ids),
    and writeLog with the unique constraint dropping duplicate runs.
  - main.go runs a 1-hour ticker; when time.Hour()==6 it invokes the
    scanner for today. Idempotent so transient restarts don't double-
    send.
  - POST /calendar/notifications/run-now for manual trigger + backfill
    (?date=YYYY-MM-DD).
  - GET /calendar/events/:id/notifications returns notification_log
    rows scoped to the owning teacher.
  - MATRIX_SERVICE_URL + EMAIL_SERVICE_URL env vars added (default
    empty = stub mode).

Frontend (studio-v2):
  - NotificationStatus component fetches /events/:id/notifications and
    renders coloured badges per (lead, audience, channel, status).
  - DayDetail mounts NotificationStatus inside each event card when
    notify_parents or notify_students is set.

Tests:
  - 6 new Go unit tests for bucketFor + Render (de/tr/fallback paths)
    + substitute(class_suffix). 89 subtests gesamt.
  - 2 new Playwright tests: badge render with mocked log, hidden when
    notifications are off.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

school-service/internal/database/database.go

@@ -227,6 +227,9 @@ func Migrate(db *DB) error {
 	// Append parent migrations (Phase 9c — see parent_migrations.go).
 	migrations = append(migrations, ParentMigrations()...)
 
+	// Append notification log (Phase 9d — see notification_migrations.go).
+	migrations = append(migrations, NotificationMigrations()...)
+
 	for _, migration := range migrations {
 		_, err := db.Pool.Exec(ctx, migration)
 		if err != nil {