fix(backup): use shared compression for database dumps

Centralize compressor selection and apply helper-image compression to dump-all database backups.

app/Support/BackupCompression.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Support;
+
+final class BackupCompression
+{
+    public static function cpuPercentage(int|string|null $configuredPercentage): int
+    {
+        $percentage = (int) $configuredPercentage;
+
+        return in_array($percentage, [25, 50, 75, 100], true) ? $percentage : 25;
+    }
+
+    public static function compressorCommand(int $cpuPercentage): string
+    {
+        $cpuPercentage = self::cpuPercentage($cpuPercentage);
+
+        return "if command -v pigz >/dev/null 2>&1; then printf 'pigz -3 -p %s' \"\$(( (\$(nproc) * {$cpuPercentage} + 99) / 100 ))\"; else printf 'gzip -3'; fi";
+    }
+}