Demo plan + Payment integrations (Stripe/PayPal/Bank)

Models & migrations:
- platform_settings table (key/value JSON store + Cache::remember 5min)
- plans: is_demo bool + trial_days int
- companies: is_demo bool

Plans:
- Demo plan seeded (is_demo=true, is_public=false, all features, 14 trial days)
- Trial 14-day plan seeded (is_public=true, basic features)
- Plan form: is_demo toggle + trial_days field
- Plan table: badge 🎬 Demo / 🎁 N zile trial

Central panel:
- PaymentSettings page (heroicon-credit-card, sort 90)
  Form sections: General, Date legale, Stripe, PayPal, Transfer bancar
  Each gateway collapsible, fields hidden until enabled toggle
  Saves to platform_settings keyed by `payments.{gateway}`
- CompanyResource: is_demo toggle + table description

Payment flow (PaymentController):
- GET  /billing                 — tenant invoices list with Pay button
- POST /pay/{sub}               — start checkout (stripe/paypal/bank)
- GET  /pay/{sub}/{success,cancel}
- POST /payments/stripe/webhook — mark paid + extend company.active_until
- POST /payments/paypal/webhook — same

Views:
- site/billing.blade.php       — invoices list with payment modal (3 methods)
- site/bank-instructions       — IBAN/BIC/reference for manual transfer
- site/checkout-stub           — placeholder until composer require stripe-php
- site/payment-{success,cancel}

Tenant panel:
- userMenuItems → "Facturile mele" link to /billing

database/migrations/2026_05_08_000050_create_platform_settings_table.php

@@ -0,0 +1,35 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration {
+    public function up(): void
+    {
+        Schema::create('platform_settings', function (Blueprint $t) {
+            $t->id();
+            $t->string('key', 100)->unique();
+            $t->json('value')->nullable();
+            $t->timestamps();
+        });
+
+        Schema::table('plans', function (Blueprint $t) {
+            $t->boolean('is_demo')->default(false)->after('is_public');
+            $t->integer('trial_days')->nullable()->after('is_demo')
+                ->comment('Days of free trial for tenants on this plan (null = no trial)');
+        });
+
+        Schema::table('companies', function (Blueprint $t) {
+            $t->boolean('is_demo')->default(false)->after('plan_id')
+                ->comment('Demo tenant — features unlocked but data may be reset');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('platform_settings');
+        Schema::table('plans', fn (Blueprint $t) => $t->dropColumn(['is_demo', 'trial_days']));
+        Schema::table('companies', fn (Blueprint $t) => $t->dropColumn('is_demo'));
+    }
+};