feat(payments): implement smart Polar subscription sync with checkout tracking

- Add provider_checkout_id column to separate checkout ID from subscription ID
   - Update Polar provider to store checkout ID separately and set subscription ID to null initially
   - Implement smart sync logic that queries Polar API when subscription ID is missing
   - Add fetchPolarSubscriptionId method to find active subscriptions via customer ID
   - Update webhook handlers to use provider_checkout_id for subscription lookup
   - Make makeAuthenticatedRequest public to enable Subscription model API access
   - Support plan metadata matching for accurate subscription identification
   - Add fallback to most recent active subscription when no exact match found

   This resolves sync button issues by properly tracking checkout vs subscription IDs
   and enables automatic subscription ID recovery when webhooks fail.

database/migrations/2025_12_06_101452_add_provider_checkout_id_to_subscriptions_table.php

@@ -0,0 +1,29 @@
+<?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('subscriptions', function (Blueprint $table) {
+            // Add provider_checkout_id column after provider_subscription_id
+            $table->string('provider_checkout_id')->nullable()->after('provider_subscription_id');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('subscriptions', function (Blueprint $table) {
+            $table->dropColumn('provider_checkout_id');
+        });
+    }
+};