Add Coach mode C3: game line-up, the last of the six coach screens

New models (events/models.py): Lineup (one per event), LineupUnit (Line 1,
Defence pair 1, ... -- coach-entered labels, no fixed sport structure since
neither Club nor Team carries one), LineupSlot (one position, optionally
filled by a member). events/services/lineup.py's publish_lineup is the
reason Attendance.AttendanceStatus.SELECTED/NOT_SELECTED existed at all --
publishing flips every slotted member to SELECTED and every other available
(non-out, non-silent) roster member to NOT_SELECTED, then notifies only the
selected players.

Placement is a native <select> per slot, batch-saved with one "Save
line-up" submit, not the design mock's drag-and-drop -- this codebase has
no established htmx interaction pattern yet (htmx.js is loaded but nothing
uses it) to build a live per-tap version on, and a reliable plain form beats
a first, unproven real-time interaction for an already-large screen.
place_member handles "swap" semantics for it: placing a member vacates any
other slot of theirs in the same lineup, bumping whoever was already in the
target slot back to the available pool.

Wires the missing pieces from C1's own docstring: the "needs you" line-up-
not-published row and the tonight card's "Line-up" button, both deferred
in that stage specifically because this model didn't exist yet.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ECGMEwrc2k4D8VQuwjstj9

events/services/lineup.py

@@ -0,0 +1,58 @@
+"""Placing players into a Lineup's slots and publishing it -- coach mode's C3
+screen (mobile/coach_views.py's CoachLineupView/CoachLineupPlaceView). Mirrors
+events.services.attendance's shape: small, focused functions the view writes
+through rather than touching the models directly.
+"""
+
+from django.utils import timezone
+from django.utils.translation import gettext_lazy as _
+
+from events.models import Attendance, LineupSlot
+from members.models import Member
+from notifications.services import notify_members
+
+#: Attendance statuses that mean "not actually available" -- these members
+#: stay exactly as they are on publish, never flipped to NOT_SELECTED, and
+#: aren't offered as placeable in the available-players pool.
+UNAVAILABLE_STATUSES = [Attendance.AttendanceStatus.ABSENT, Attendance.AttendanceStatus.EXCUSED, Attendance.AttendanceStatus.NO_RESPONSE]
+
+
+def place_member(lineup, slot, member):
+    """Tap-to-place: ``member`` moves into ``slot``, vacating any other slot
+    of theirs in the same ``lineup`` first (a member is only ever in one slot
+    at a time). Whoever was already in ``slot``, if anyone, is simply bumped
+    back to the available pool -- the tap equivalent of the mock's "slots
+    accept one player and swap on drop", without true drag-and-drop's two-way
+    swap (see LineupSlot's own docstring for why tap-to-place instead of
+    drag-and-drop at all)."""
+    LineupSlot.objects.filter(unit__lineup=lineup, member=member).exclude(pk=slot.pk).update(member=None)
+    slot.member = member
+    slot.save(update_fields=["member"])
+
+
+def clear_slot(slot):
+    slot.member = None
+    slot.save(update_fields=["member"])
+
+
+def publish_lineup(lineup):
+    """Marks the lineup published and writes it into the game record via
+    Attendance -- the reason AttendanceStatus.SELECTED/NOT_SELECTED exist,
+    previously unused anywhere. Every slotted member becomes SELECTED; every
+    other member with an Attendance row for this event who was actually
+    available (not out/silent, see UNAVAILABLE_STATUSES) becomes
+    NOT_SELECTED. Notifies only the selected players."""
+    lineup.published_at = timezone.now()
+    lineup.save(update_fields=["published_at"])
+
+    selected_member_ids = set(LineupSlot.objects.filter(unit__lineup=lineup, member__isnull=False).values_list("member_id", flat=True))
+
+    Attendance.objects.filter(event=lineup.event, member_id__in=selected_member_ids).update(status=Attendance.AttendanceStatus.SELECTED)
+    Attendance.objects.filter(event=lineup.event).exclude(member_id__in=selected_member_ids).exclude(status__in=UNAVAILABLE_STATUSES).update(status=Attendance.AttendanceStatus.NOT_SELECTED)
+
+    selected_members = Member.objects.filter(pk__in=selected_member_ids)
+    if selected_members:
+        body = _("You're in the line-up for %(event)s.") % {"event": lineup.event.title}
+        notify_members(selected_members, club=lineup.event.club, title=_("Line-up published"), body=body, source=lineup.event)
+
+    return lineup