feat(storage): S3 相容物件儲存支援 + 一次性遷移指令

實作 cloud-ready-s3-storage 的程式碼部分（tasks 1-3）：

- config/filesystems.php：public disk 的 driver 改吃 FILESYSTEM_DISK env，
  切換為 s3 時不需改動既有 6 個 Storage::disk('public') 呼叫點
- .env.example：FILESYSTEM_DISK 維持 local 預設（本機無 S3 服務），補齊
  AWS_ENDPOINT/AWS_URL/AWS_USE_PATH_STYLE_ENDPOINT 供 R2 等服務使用
- 新增 storage:migrate-to-s3 指令：一次性把 storage/app/public 既有檔案
  上傳到 S3，來源固定讀本機磁碟（不受 FILESYSTEM_DISK 影響），支援
  --dry-run，失敗不中斷且不刪除本機檔案
- 新增測試：遷移指令（上傳/dry-run/部分失敗）+ public disk 在 local
  driver 下零 AWS credentials 也能正常運作

239 tests passed / 578 assertions，容器內驗證無回歸。

R2 環境準備、VPS 部署與實際切換（tasks 4-6）待 Hank 自行處理。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011LpcY9b7y9x4fusHBTXciQ

tests/Feature/FilesystemPublicDiskTest.php

@@ -0,0 +1,43 @@
+<?php
+
+namespace Tests\Feature;
+
+use Illuminate\Support\Facades\Config;
+use Illuminate\Support\Facades\Storage;
+use Tests\TestCase;
+
+class FilesystemPublicDiskTest extends TestCase
+{
+    protected function tearDown(): void
+    {
+        @unlink(storage_path('app/public/filesystem-public-disk-test.txt'));
+
+        parent::tearDown();
+    }
+
+    public function test_public_disk_works_on_local_driver_without_aws_credentials(): void
+    {
+        Config::set('filesystems.disks.public.driver', 'local');
+        Config::set('filesystems.disks.public.key', null);
+        Config::set('filesystems.disks.public.secret', null);
+        Config::set('filesystems.disks.public.region', null);
+        Config::set('filesystems.disks.public.bucket', null);
+        Config::set('filesystems.disks.public.endpoint', null);
+        Storage::forgetDisk('public');
+
+        Storage::disk('public')->put('filesystem-public-disk-test.txt', 'ok');
+
+        $this->assertTrue(Storage::disk('public')->exists('filesystem-public-disk-test.txt'));
+
+        Storage::disk('public')->delete('filesystem-public-disk-test.txt');
+    }
+
+    public function test_public_disk_driver_follows_filesystem_disk_env(): void
+    {
+        $this->assertSame(
+            env('FILESYSTEM_DISK', 'local'),
+            config('filesystems.disks.public.driver'),
+            'public disk 的 driver 應完全跟隨 FILESYSTEM_DISK env（未設定時預設 local）'
+        );
+    }
+}

tests/Feature/MigrateStorageToS3Test.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace Tests\Feature;
+
+use Illuminate\Support\Facades\Storage;
+use Mockery;
+use RuntimeException;
+use Tests\TestCase;
+
+class MigrateStorageToS3Test extends TestCase
+{
+    private array $createdFiles = [];
+
+    protected function tearDown(): void
+    {
+        foreach ($this->createdFiles as $relativePath) {
+            @unlink(storage_path('app/public/'.$relativePath));
+        }
+        $this->createdFiles = [];
+
+        parent::tearDown();
+    }
+
+    private function putLocalFile(string $relativePath, string $contents = 'test-content'): void
+    {
+        $fullPath = storage_path('app/public/'.$relativePath);
+        @mkdir(dirname($fullPath), 0777, true);
+        file_put_contents($fullPath, $contents);
+        $this->createdFiles[] = $relativePath;
+    }
+
+    public function test_uploads_existing_local_files_to_s3(): void
+    {
+        Storage::fake('s3');
+        $this->putLocalFile('migrate-test/one.txt', 'file-one');
+        $this->putLocalFile('migrate-test/two.txt', 'file-two');
+
+        $this->artisan('storage:migrate-to-s3')->assertSuccessful();
+
+        Storage::disk('s3')->assertExists('migrate-test/one.txt');
+        Storage::disk('s3')->assertExists('migrate-test/two.txt');
+    }
+
+    public function test_dry_run_lists_files_without_uploading(): void
+    {
+        Storage::fake('s3');
+        $this->putLocalFile('migrate-test/dry.txt');
+
+        $this->artisan('storage:migrate-to-s3', ['--dry-run' => true])->assertSuccessful();
+
+        Storage::disk('s3')->assertMissing('migrate-test/dry.txt');
+    }
+
+    public function test_no_files_to_migrate_still_succeeds(): void
+    {
+        Storage::fake('s3');
+
+        $this->artisan('storage:migrate-to-s3')->assertSuccessful();
+    }
+
+    public function test_reports_failure_and_does_not_stop_on_partial_upload_error(): void
+    {
+        $this->putLocalFile('migrate-test/ok.txt', 'ok');
+        $this->putLocalFile('migrate-test/bad.txt', 'bad');
+
+        // storage/app/public 是共用的本機目錄，可能已存在其他測試無關的檔案（如手動測試留下的
+        // 上傳圖片），所以這裡不斷言呼叫次數，只鎖定我們自己建立的兩個檔案的行為，其餘路徑一律放行。
+        $mockDisk = Mockery::mock();
+        $mockDisk->shouldReceive('put')
+            ->with('migrate-test/bad.txt', Mockery::any())
+            ->once()
+            ->andThrow(new RuntimeException('simulated network failure'));
+        $mockDisk->shouldReceive('put')
+            ->withArgs(fn (string $path) => $path !== 'migrate-test/bad.txt')
+            ->andReturn(true);
+        $mockDisk->shouldReceive('exists')->andReturn(true);
+
+        Storage::partialMock()->shouldReceive('disk')->with('s3')->andReturn($mockDisk);
+
+        $this->artisan('storage:migrate-to-s3')->assertFailed();
+    }
+}