feat(backups): add configurable CPU usage for volume compression

Add server-level compression CPU presets for volume backups and close the private key modal after saving.

database/migrations/2026_08_14_074053_add_backup_compression_cpu_percentage_to_server_settings_table.php

@@ -0,0 +1,28 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    /**
+     * Run the migrations.
+     */
+    public function up(): void
+    {
+        Schema::table('server_settings', function (Blueprint $table) {
+            $table->unsignedTinyInteger('backup_compression_cpu_percentage')->default(25);
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('server_settings', function (Blueprint $table) {
+            $table->dropColumn('backup_compression_cpu_percentage');
+        });
+    }
+};