Never drop an enrolled class from upcoming lessons; delete a guardian's children with them; pin the panel's line spacing

Three fixes from testing the branch.

A group class was only listed when its schedule resolved to exact
datetimes, which needs a class time *and* a duration — both optional on
the offering form, and the schedule note exists precisely so a studio can
write "Tuesdays 4:00pm" instead. A class configured that way vanished
from the list, which is the one thing this feature must never do. So
Offering::sessionStarts() splits "when does it meet" from "how long does
it run" (sessionWindows() is that plus the duration, unchanged), and
SessionSchedule degrades instead of disappearing: dated rows with an open
end when there is no duration, and a single row carrying
Offering::scheduleLabel() when there is no time to derive dates from.
Only a class whose last day has passed drops out.

Deleting a guardian now deletes the children linked to them, releasing
each one's lessons and enrolments first. A child account is login-less
and exists only so the guardian has somebody to book for; without the
guardian nobody can reach it, book for it, or be billed for it, so it was
left stranded on the roster still holding slots. A `handled` set makes
the re-entrant delete_user each child deletion fires a no-op, and stops a
circular link recursing.

The upcoming panel never stated its own line-height, so a theme setting
line-height: 0 above it — the usual icon-font reset — was inherited
straight through. Below 1 that produces both reported symptoms at once:
stacked lines overlap, and the status pill's background is shorter than
the text in it. Pinned at the same id-level specificity as the rest.

Tests: composer test (863), composer lint, composer cs all pass.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/Auth/StudentController.php

@@ -205,6 +205,7 @@ class StudentController {
 		return [
 			'id'         => (int) $lesson->id,
 			'kind'       => 'lesson',
+			'schedule'   => null,
 			'start_dt'   => $slot ? $slot->startDt : '',
 			'end_dt'     => $slot ? $slot->endDt : '',
 			'offering'   => $offering ? $offering->title : '—',
@@ -231,6 +232,9 @@ class StudentController {
 					'kind'       => SessionSchedule::KIND,
 					'start_dt'   => $session['start_dt'],
 					'end_dt'     => $session['end_dt'],
+					// Set when the class has no time to put on a clock; shown in the
+					// When column in place of a date. See GroupClass\SessionSchedule.
+					'schedule'   => $session['schedule'],
 					'offering'   => $session['offering_title'],
 					'instructor' => $instructor ? $instructor->display_name : (string) $session['instructor_id'],
 					'status'     => $session['status'],