feat: smart assign person dialog with conflict details and assignable-persons endpoint

Add GET /events/{event}/shifts/{shift}/assignable-persons endpoint that
returns approved persons with availability status, conflict details, and
already-assigned flags. Improve ShiftAssignmentService conflict errors to
include section name, time slot, and time range. Replace both assign
dialogs with a new AssignPersonDialog featuring search, crowd type
filtering, availability toggle, and inline conflict warnings.

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

api/app/Http/Controllers/Api/V1/ShiftAssignmentController.php

@@ -4,12 +4,15 @@ declare(strict_types=1);
 
 namespace App\Http\Controllers\Api\V1;
 
+use App\Enums\PersonStatus;
 use App\Enums\ShiftAssignmentStatus;
 use App\Http\Controllers\Controller;
 use App\Http\Requests\Api\V1\BulkApproveShiftAssignmentRequest;
 use App\Http\Requests\Api\V1\RejectShiftAssignmentRequest;
 use App\Http\Resources\Api\V1\ShiftAssignmentResource;
 use App\Models\Event;
+use App\Models\Person;
+use App\Models\Shift;
 use App\Models\ShiftAssignment;
 use App\Services\ShiftAssignmentService;
 use Illuminate\Http\JsonResponse;
@@ -98,4 +101,72 @@ final class ShiftAssignmentController extends Controller
 
         return $this->success($results);
     }
+
+    public function assignablePersons(Event $event, Shift $shift): JsonResponse
+    {
+        Gate::authorize('viewAny', [ShiftAssignment::class, $event]);
+
+        $festivalEventId = $event->parent_event_id ?? $event->id;
+        $timeSlotId = $shift->time_slot_id;
+        $shiftId = $shift->id;
+
+        // Get all conflict assignments for this time slot in one query
+        $conflicts = ShiftAssignment::where('time_slot_id', $timeSlotId)
+            ->whereIn('status', [
+                ShiftAssignmentStatus::PENDING_APPROVAL,
+                ShiftAssignmentStatus::APPROVED,
+            ])
+            ->with(['shift.festivalSection', 'shift.timeSlot'])
+            ->get()
+            ->keyBy('person_id');
+
+        // Get all assignments for THIS shift in one query
+        $alreadyAssigned = ShiftAssignment::where('shift_id', $shiftId)
+            ->whereNotIn('status', [
+                ShiftAssignmentStatus::REJECTED,
+                ShiftAssignmentStatus::CANCELLED,
+            ])
+            ->pluck('person_id')
+            ->flip();
+
+        $persons = Person::where('event_id', $festivalEventId)
+            ->where('status', PersonStatus::APPROVED)
+            ->with('crowdType')
+            ->orderBy('name')
+            ->get()
+            ->map(function (Person $person) use ($conflicts, $alreadyAssigned, $shiftId) {
+                $isAlreadyAssigned = $alreadyAssigned->has($person->id);
+                $conflict = $conflicts->get($person->id);
+                $hasConflict = $conflict && $conflict->shift_id !== $shiftId;
+
+                return [
+                    'id' => $person->id,
+                    'name' => $person->name,
+                    'email' => $person->email,
+                    'status' => $person->status,
+                    'crowd_type' => $person->crowdType ? [
+                        'id' => $person->crowdType->id,
+                        'name' => $person->crowdType->name,
+                        'system_type' => $person->crowdType->system_type,
+                    ] : null,
+                    'is_available' => ! $hasConflict && ! $isAlreadyAssigned,
+                    'already_assigned' => $isAlreadyAssigned,
+                    'conflict' => $hasConflict ? [
+                        'section_name' => $conflict->shift->festivalSection->name,
+                        'shift_title' => $conflict->shift->title ?? $conflict->shift->festivalSection->name,
+                        'time_slot_name' => $conflict->shift->timeSlot->name,
+                        'time' => $conflict->shift->timeSlot->start_time
+                            . '–' . $conflict->shift->timeSlot->end_time,
+                    ] : null,
+                ];
+            })
+            ->sortBy([
+                ['already_assigned', 'asc'],
+                ['is_available', 'desc'],
+                ['name', 'asc'],
+            ])
+            ->values();
+
+        return response()->json(['data' => $persons]);
+    }
 }