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/models.py

@@ -198,6 +198,72 @@ class Attendance(UUIDModel):
         return f"{self.event} - {self.member}"
 
 
+class Lineup(UUIDModel):
+    """A game's line-up -- coach mode's C3 screen (mobile/coach_views.py's
+    CoachLineupView). One per event; ``units`` (Line 1, Defence pair 1, ...)
+    hold ordered ``slots``, each optionally filled by a member. Publishing
+    (events.services.lineup.publish_lineup) flips every slotted member's
+    Attendance.status to SELECTED and every other available roster member's
+    to NOT_SELECTED -- the reason those two statuses exist on Attendance in
+    the first place, previously unused."""
+
+    event = models.OneToOneField(Event, on_delete=models.CASCADE, related_name="lineup", verbose_name=_("event"))
+    team = models.ForeignKey(Team, on_delete=models.CASCADE, related_name="lineups", verbose_name=_("team"))
+    published_at = models.DateTimeField(_("published at"), null=True, blank=True)
+    created_by = models.ForeignKey(Member, on_delete=models.SET_NULL, null=True, blank=True, related_name="created_lineups", verbose_name=_("created by"))
+
+    class Meta:
+        verbose_name = _("line-up")
+        verbose_name_plural = _("line-ups")
+
+    def __str__(self):
+        return f"{self.team} - {self.event}"
+
+    def clean(self):
+        validate_club_scope(self, self.event.club_id if self.event_id else None, same_club_fields=("team",))
+
+
+class LineupUnit(UUIDModel):
+    """One group of slots within a Lineup -- "Line 1", "Defence pair 1", ...
+    Coach-entered labels, not a fixed sport structure: neither Club nor Team
+    carries a sport field to derive one from."""
+
+    lineup = models.ForeignKey(Lineup, on_delete=models.CASCADE, related_name="units", verbose_name=_("line-up"))
+    label = models.CharField(_("label"), max_length=100)
+    ordering = models.PositiveSmallIntegerField(_("ordering"), default=0)
+
+    class Meta:
+        verbose_name = _("line-up unit")
+        verbose_name_plural = _("line-up units")
+        ordering = ["ordering"]
+
+    def __str__(self):
+        return self.label
+
+
+class LineupSlot(UUIDModel):
+    """One position within a LineupUnit, optionally filled by a member.
+    Placement/swapping is tap-to-place (mobile/coach_views.py's
+    CoachLineupPlaceView), not drag-and-drop -- see that view's own
+    docstring for why. A member is only ever in one slot per lineup at a
+    time; enforcing that (clearing any prior slot of theirs on placement) is
+    the placement service's job, not a DB constraint -- "which unit a member
+    is in" spans this table's own FK, awkward to express as a single
+    UniqueConstraint."""
+
+    unit = models.ForeignKey(LineupUnit, on_delete=models.CASCADE, related_name="slots", verbose_name=_("unit"))
+    ordering = models.PositiveSmallIntegerField(_("ordering"), default=0)
+    member = models.ForeignKey(Member, on_delete=models.SET_NULL, null=True, blank=True, related_name="lineup_slots", verbose_name=_("member"))
+
+    class Meta:
+        verbose_name = _("line-up slot")
+        verbose_name_plural = _("line-up slots")
+        ordering = ["ordering"]
+
+    def __str__(self):
+        return f"{self.unit} - {self.member or 'empty'}"
+
+
 class EventReferee(UUIDModel):
     """One referee assigned to one (home) game -- either a club member
     (``member`` set) or an external referee logged by name only