refactor(backup): validate database backup upload file type and size

Add allowlist of backup file extensions (sql, sql.gz, tar, tgz, zip,
dump, bak, bson, archive, bz2, xz, and compound variants) and enforce
a 10 GiB maximum file size on the backup upload endpoint. Validation
runs early on each chunk using the dropzone metadata and again on the
assembled file. Also drops the unused createFilename helper and the
commented-out S3 block.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/Feature/DatabaseBackupUploadValidationTest.php

@@ -0,0 +1,62 @@
+<?php
+
+use App\Http\Controllers\UploadController;
+
+function invokeHasAllowedExtension(string $name): bool
+{
+    $method = new ReflectionMethod(UploadController::class, 'hasAllowedExtension');
+    $method->setAccessible(true);
+
+    return $method->invoke(null, $name);
+}
+
+test('hasAllowedExtension accepts supported extensions', function (string $name) {
+    expect(invokeHasAllowedExtension($name))->toBeTrue();
+})->with([
+    'plain sql' => ['backup.sql'],
+    'uppercase sql' => ['BACKUP.SQL'],
+    'compound sql.gz' => ['backup.sql.gz'],
+    'compound tar.gz' => ['backup.tar.gz'],
+    'tgz' => ['archive.tgz'],
+    'zip' => ['dump.zip'],
+    'tar' => ['dump.tar'],
+    'gz' => ['data.gz'],
+    'dump' => ['data.dump'],
+    'bak' => ['data.bak'],
+    'bson' => ['data.bson'],
+    'bson.gz' => ['data.bson.gz'],
+    'archive' => ['data.archive'],
+    'archive.gz' => ['data.archive.gz'],
+    'bz2' => ['data.bz2'],
+    'xz' => ['data.xz'],
+]);
+
+test('hasAllowedExtension rejects unsupported or empty stems', function (string $name) {
+    expect(invokeHasAllowedExtension($name))->toBeFalse();
+})->with([
+    'php' => ['shell.php'],
+    'phtml' => ['shell.phtml'],
+    'sh' => ['run.sh'],
+    'exe' => ['malware.exe'],
+    'elf binary no ext' => ['payload'],
+    'html' => ['index.html'],
+    'bare compound without stem' => ['.sql.gz'],
+    'bare extension' => ['.sql'],
+    'empty string' => [''],
+    'misleading double ext' => ['shell.php.sql-evil'],
+]);
+
+test('MAX_BYTES constant is 10 GiB', function () {
+    $constant = (new ReflectionClass(UploadController::class))->getConstant('MAX_BYTES');
+    expect($constant)->toBe(10 * 1024 * 1024 * 1024);
+});
+
+test('ALLOWED_EXTENSIONS does not include executable formats', function () {
+    $constant = (new ReflectionClass(UploadController::class))->getConstant('ALLOWED_EXTENSIONS');
+    expect($constant)->toBeArray();
+
+    $forbidden = ['php', 'phtml', 'php5', 'sh', 'bash', 'exe', 'js', 'html', 'htm', 'pl', 'py'];
+    foreach ($forbidden as $bad) {
+        expect($constant)->not->toContain($bad);
+    }
+});