新增單位管理以及一些功能修正

database/migrations/2026_01_08_103000_create_units_table.php

@@ -0,0 +1,29 @@
+<?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::create('units', function (Blueprint $table) {
+            $table->id();
+            $table->string('name')->unique()->comment('單位名稱');
+            $table->string('code')->nullable()->comment('單位代碼 (如: kg)');
+            $table->timestamps();
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('units');
+    }
+};