add set scheduling api

backend/database/migrations/2026_08_10_000000_create_schedules_table.php

@@ -0,0 +1,30 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('schedules', function (Blueprint $table): void {
+            $table->id();
+            $table->foreignId('user_id')
+                ->constrained('users')
+                ->restrictOnDelete();
+            $table->foreignId('set_id')
+                ->constrained('sets')
+                ->restrictOnDelete();
+            $table->string('element_kind');
+            $table->date('start_date');
+            $table->date('target_date');
+            $table->index(['user_id', 'id']);
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('schedules');
+    }
+};

backend/database/migrations/2026_08_10_000001_create_schedule_assignments_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
+{
+    public function up(): void
+    {
+        Schema::create(
+            'schedule_assignments',
+            function (Blueprint $table): void {
+                $table->id();
+                $table->foreignId('schedule_id')
+                    ->constrained('schedules')
+                    ->cascadeOnDelete();
+                $table->foreignId('element_id')
+                    ->constrained('elements')
+                    ->restrictOnDelete();
+                $table->date('scheduled_date');
+                $table->unsignedInteger('position');
+                $table->unique(['schedule_id', 'element_id']);
+                $table->unique(['schedule_id', 'position']);
+                $table->index([
+                    'schedule_id',
+                    'scheduled_date',
+                    'position',
+                ]);
+            },
+        );
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('schedule_assignments');
+    }
+};