feat(offers): 補齊 provider-verification 可見性缺口——子端點過濾與預約入口檢查

實作 openspec change provider-verification-gaps（8/8 tasks）：
- schedules/reviews publicList 套用 visibleToPublic，隱藏課程回 404
- MemberBookingController::store Layer 1 擋未驗證教練課程的新預約（422）
- 政策：教練被取消驗證只擋新預約，既有 pending/confirmed/completed 照常
- 主規格 Notes 已知限制轉為正式 Requirements
- 測試 +5（可見性子端點 3、預約入口 2），既有 booking/review 測試 helper
  補 verified ProviderProfile
- 容器內全套件 151 passed / 388 assertions；另以 demo 資料端到端驗證
  （已驗證教練 200/200/200、未驗證 404/404/404）

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tests/Feature/BookingOversellTest.php

@@ -7,6 +7,7 @@ use App\Enums\ScheduleStatus;
 use App\Models\Booking;
 use App\Models\CourseSchedule;
 use App\Models\DivingOffer;
+use App\Models\ProviderProfile;
 use App\Models\User;
 use Illuminate\Foundation\Testing\RefreshDatabase;
 use Illuminate\Support\Facades\Notification;
@@ -33,6 +34,11 @@ class BookingOversellTest extends TestCase
     {
         $provider = User::factory()->create(['role' => 'provider']);
 
+        ProviderProfile::create([
+            'user_id'     => $provider->id,
+            'is_verified' => true,
+        ]);
+
         $offer = DivingOffer::create([
             'provider_id' => $provider->id,
             'title'       => 'Oversell Course',