feat(proxy): make the Traefik certificate resolver configurable per server

Coolify always added tls.certresolver=letsencrypt to generated HTTPS
routers, so Traefik logged errors when the proxy used its own
certificates (for example Cloudflare Origin CA) without that resolver.
Add a server setting (default letsencrypt) in the proxy page and API.
An empty value omits the resolver from resource labels, the Coolify
dashboard routes, and the catch-all router.

Closes #12138

database/migrations/2026_10_11_075120_add_traefik_certificate_resolver_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->string('traefik_certificate_resolver')->nullable()->default('letsencrypt');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('server_settings', function (Blueprint $table) {
+            $table->dropColumn('traefik_certificate_resolver');
+        });
+    }
+};