feat: add shift management functionality

database/migrations/2026_08_26_000000_create_shifts_table.php

@@ -0,0 +1,38 @@
+<?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('shifts', function (Blueprint $table) {
+            $table->id();
+            $table->string('day_of_week')->nullable();
+            $table->date('date')->nullable();
+            $table->time('start_time');
+            $table->time('end_time');
+            $table->boolean('is_active')->default(true);
+            $table->timestamps();
+
+            $table->foreignId('user_id')->nullable()->constrained('users')->nullOnDelete();
+            $table->foreignId('created_by')->nullable()->constrained('users')->nullOnDelete();
+
+            $table->index(['day_of_week', 'is_active']);
+            $table->index(['date', 'is_active']);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('shifts');
+    }
+};