feat: allow organizer overbooking with confirmation dialog

Remove capacity and status validation from organizer assign flow so
organizers can intentionally overbook shifts. Log overbooked assignments
for audit trail. Volunteer claims still enforce hard limits. Frontend
shows a warning banner when a shift is full and requires confirmation
before overbooking.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Services/ShiftAssignmentService.php

@@ -70,10 +70,26 @@ final class ShiftAssignmentService
     public function assign(Shift $shift, Person $person, User $assignedBy): ShiftAssignment
     {
         return DB::transaction(function () use ($shift, $person, $assignedBy): ShiftAssignment {
-            $this->validateShiftIsOpen($shift);
-            $this->validateAssignCapacity($shift);
             $this->validateNoConflict($shift, $person);
 
+            // Log overbooking for audit trail (organizers may intentionally overbook)
+            $filledSlots = $shift->shiftAssignments()
+                ->where('status', ShiftAssignmentStatus::APPROVED)
+                ->count();
+
+            if ($filledSlots >= $shift->slots_total) {
+                activity('shift_assignment')
+                    ->causedBy($assignedBy)
+                    ->performedOn($shift)
+                    ->withProperties([
+                        'filled_slots' => $filledSlots,
+                        'slots_total' => $shift->slots_total,
+                        'person_id' => $person->id,
+                        'person_name' => $person->name,
+                    ])
+                    ->log('shift.overbooked_assignment');
+            }
+
             $assignment = $shift->shiftAssignments()->create([
                 'person_id' => $person->id,
                 'time_slot_id' => $shift->time_slot_id,