Auto-deduct spice inventory when batch is created/updated/deleted

- Add size_id, units_produced, quantity_g to batches table
- quantity_g auto-calculated from units × packing size on save
- Batch model deducts spice quantities on create, reverses on delete,
  recalculates on update when relevant fields change
- Batch form shows live total weight preview
- Chargen table shows units + grams produced

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

database/migrations/2026_09_12_033131_add_production_fields_to_batches.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::table('batches', function (Blueprint $table) {
+            $table->foreignId('size_id')->nullable()->after('product_id')
+                  ->constrained('products_sizes')->nullOnDelete();
+            $table->unsignedInteger('units_produced')->nullable()->after('size_id');
+            $table->decimal('quantity_g', 10, 2)->nullable()->after('units_produced');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('batches', function (Blueprint $table) {
+            $table->dropForeign(['size_id']);
+            $table->dropColumn(['size_id', 'units_produced', 'quantity_g']);
+        });
+    }
+};