记录所有人在线时长：允许 user_position_id 为空，移除记录日志时的职务判断

database/migrations/2026_03_18_214320_make_user_position_id_nullable_on_position_duty_logs_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('position_duty_logs', function (Blueprint $table) {
+            $table->unsignedBigInteger('user_position_id')->nullable()->change();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('position_duty_logs', function (Blueprint $table) {
+            $table->unsignedBigInteger('user_position_id')->nullable(false)->change();
+        });
+    }
+};