Billing Phase 1: Tarifstatus-Datenmodell und Tariflogik je Mandant

Vorbereitung fuer Stripe Billing (Zahlungseinzug) + bestehendes Dolibarr
des Kunden (Rechnungsstellung/Buchhaltung) statt eines eigenen Rechnungs-
systems oder eines zusaetzlichen ERP nur fuer Kaffeeliste - Begruendung
in docs/billing.md.

- Neue Tabelle tenant_billing (plan_code, subscription_status, sowie
  bereits vorbereitete, noch ungenutzte Felder fuer Stripe/Dolibarr-IDs).
- app/billing.php: billing_plans() als einzige Quelle der Tarifstufen
  (synchron mit preise.php), billing_required_plan_code() anhand aktiver
  Teilnehmerzahl, billing_check_tenant() vergleicht gebuchten mit
  benoetigtem Tarif - rein informativ, kein Enforcement, solange Stripe
  nicht angebunden ist.
- Neue Mandanten starten automatisch auf plan_code='free' bei der
  Registrierung.
- mandant-einstellungen.php zeigt Owner/Admin ihren aktuellen Tarif und
  Teilnehmerstand, mit Hinweis bei Bedarf einer hoeheren Stufe.
- Back-Office zeigt zusaetzlich zur Mandantenliste den gebuchten und
  (falls abweichend) den tatsaechlich benoetigten Tarif.

Live getestet: Tarifgrenzen (10/25/50/150) mit einem Mandanten unter und
einem ueber dem Freikontingent geprueft, UI in Mandant-Einstellungen und
Back-Office verifiziert. Alle M8-Isolations-/Rollenmatrix-Tests weiterhin
gruen.

Phase 2 (Stripe) und Phase 3 (Dolibarr-Sync) folgen, sobald Test-Keys
beziehungsweise Sandbox-Zugang vorliegen.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/billing.php

@@ -0,0 +1,98 @@
+<?php
+
+declare(strict_types=1);
+
+require_once __DIR__ . '/bootstrap.php';
+
+/**
+ * Single source of truth for the pricing tiers, matching preise.php and
+ * agb.php. max_participants = null means "no upper limit defined, contact
+ * us" (the "auf Anfrage" tier).
+ *
+ * @return array<string, array{label: string, max_participants: ?int, price_cents: int}>
+ */
+function billing_plans(): array
+{
+    return [
+        'free' => ['label' => 'Kostenlos', 'max_participants' => 10, 'price_cents' => 0],
+        'basic' => ['label' => 'Basic', 'max_participants' => 25, 'price_cents' => 399],
+        'plus' => ['label' => 'Plus', 'max_participants' => 50, 'price_cents' => 799],
+        'pro' => ['label' => 'Pro', 'max_participants' => 150, 'price_cents' => 1299],
+        'enterprise' => ['label' => 'Enterprise (auf Anfrage)', 'max_participants' => null, 'price_cents' => 0],
+    ];
+}
+
+/**
+ * Returns the cheapest plan whose participant limit still covers
+ * $activeParticipantCount. Used both to show customers which plan they
+ * need and, once Stripe is wired up, to detect required upgrades.
+ */
+function billing_required_plan_code(int $activeParticipantCount): string
+{
+    foreach (billing_plans() as $code => $plan) {
+        if ($plan['max_participants'] === null || $activeParticipantCount <= $plan['max_participants']) {
+            return $code;
+        }
+    }
+
+    return 'enterprise';
+}
+
+function billing_count_active_participants(PDO $pdo, int $tenantId): int
+{
+    $stmt = $pdo->prepare('SELECT COUNT(*) FROM participants WHERE tenant_id = ? AND active = 1');
+    $stmt->execute([$tenantId]);
+
+    return (int)$stmt->fetchColumn();
+}
+
+/**
+ * @return array{tenant_id: int, plan_code: string, subscription_status: string, stripe_customer_id: ?string, stripe_subscription_id: ?string, current_period_end: ?string}
+ */
+function billing_fetch_or_init(PDO $pdo, int $tenantId): array
+{
+    $stmt = $pdo->prepare('SELECT * FROM tenant_billing WHERE tenant_id = ?');
+    $stmt->execute([$tenantId]);
+    $row = $stmt->fetch();
+
+    if ($row === false) {
+        $pdo->prepare("INSERT INTO tenant_billing (tenant_id, plan_code, subscription_status) VALUES (?, 'free', 'active')")
+            ->execute([$tenantId]);
+
+        return [
+            'tenant_id' => $tenantId,
+            'plan_code' => 'free',
+            'subscription_status' => 'active',
+            'stripe_customer_id' => null,
+            'stripe_subscription_id' => null,
+            'current_period_end' => null,
+        ];
+    }
+
+    return $row;
+}
+
+/**
+ * Compares the tenant's currently booked plan against what their active
+ * participant count actually requires. Purely informational until the
+ * Stripe integration lands — nothing here blocks usage or auto-upgrades.
+ *
+ * @return array{current_plan: string, required_plan: string, active_participants: int, needs_upgrade: bool}
+ */
+function billing_check_tenant(PDO $pdo, int $tenantId): array
+{
+    $billing = billing_fetch_or_init($pdo, $tenantId);
+    $activeCount = billing_count_active_participants($pdo, $tenantId);
+    $requiredPlan = billing_required_plan_code($activeCount);
+
+    $plans = array_keys(billing_plans());
+    $currentRank = array_search($billing['plan_code'], $plans, true);
+    $requiredRank = array_search($requiredPlan, $plans, true);
+
+    return [
+        'current_plan' => $billing['plan_code'],
+        'required_plan' => $requiredPlan,
+        'active_participants' => $activeCount,
+        'needs_upgrade' => $requiredRank !== false && $currentRank !== false && $requiredRank > $currentRank,
+    ];
+}

app/platform-admin.php

@@ -55,6 +55,7 @@ function app_backoffice_fetch_tenants(PDO $pdo): array
     $stmt = $pdo->query(
         "SELECT
             t.id, t.slug, t.name, t.status, t.created_at,
+            COALESCE(tb.plan_code, 'free') AS plan_code,
             COUNT(p.id) AS participant_count,
             COALESCE(SUM(p.active), 0) AS active_participant_count,
             COALESCE((
@@ -64,7 +65,8 @@ function app_backoffice_fetch_tenants(PDO $pdo): array
             ), 0) AS balance_cents
          FROM tenants t
          LEFT JOIN participants p ON p.tenant_id = t.id
-         GROUP BY t.id, t.slug, t.name, t.status, t.created_at
+         LEFT JOIN tenant_billing tb ON tb.tenant_id = t.id
+         GROUP BY t.id, t.slug, t.name, t.status, t.created_at, tb.plan_code
          ORDER BY t.created_at DESC"
     );
 

app/saas-auth.php

@@ -5,6 +5,7 @@ declare(strict_types=1);
 require_once __DIR__ . '/bootstrap.php';
 require_once __DIR__ . '/database.php';
 require_once __DIR__ . '/faq.php';
+require_once __DIR__ . '/billing.php';
 
 function saas_email_norm(string $email): string
 {
@@ -1061,6 +1062,7 @@ function saas_register_tenant_owner(PDO $pdo, array $input): array
         $stmt->execute([$tenantId, 20, 1, 0, '']);
 
         faq_seed_default_entries($pdo, $tenantId);
+        billing_fetch_or_init($pdo, $tenantId);
 
         if ($existingUser === false) {
             $stmt = $pdo->prepare(