Add Multi-Tenant SaaS foundation for customer management

Phase 1 implementation includes:

Database:
- schema.sql with tables for tenants, domains, settings, branding,
  streams, users, subscriptions, plans, invoices, viewer_stats

Core Classes (src/Core/):
- Database.php: PDO wrapper with singleton pattern
- TenantResolver.php: Domain-to-tenant resolution with fallback

Tenant Classes (src/Tenant/):
- TenantManager.php: CRUD operations for tenants
- TenantSettingsManager.php: DB-based settings per tenant

Configuration:
- config.example.php: Template for database/stripe/mail config
- bootstrap.php: Initializes multi-tenant environment
- .gitignore: Excludes config.php and cache files

Integration:
- SettingsManager.php: Added saas_features toggles (all off by default)
- index.php: Uses getSiteConfig() from bootstrap when multi-tenant enabled,
  falls back to legacy hardcoded domains when disabled

All SaaS features are disabled by default (saas_features.multi_tenant_enabled = false),
ensuring zero breaking changes to existing installations.

aurora-livecam/config.example.php

@@ -0,0 +1,59 @@
+<?php
+/**
+ * Aurora Livecam - Konfigurationsdatei
+ *
+ * Kopiere diese Datei zu config.php und passe die Werte an.
+ * WICHTIG: config.php niemals in Git committen!
+ */
+
+return [
+    // Datenbank-Konfiguration
+    'database' => [
+        'host' => 'localhost',
+        'port' => 3306,
+        'database' => 'aurora_livecam',
+        'username' => 'root',
+        'password' => '',
+        'charset' => 'utf8mb4',
+    ],
+
+    // Anwendungs-Einstellungen
+    'app' => [
+        'name' => 'Aurora Livecam',
+        'url' => 'https://aurora-weather-livecam.com',
+        'debug' => false,
+        'timezone' => 'Europe/Zurich',
+    ],
+
+    // Multi-Tenant Einstellungen
+    'tenant' => [
+        'default_subdomain_suffix' => '.aurora-livecam.com',
+        'allow_custom_domains' => true,
+        'trial_days' => 14,
+    ],
+
+    // Stripe (für Billing)
+    'stripe' => [
+        'public_key' => '',
+        'secret_key' => '',
+        'webhook_secret' => '',
+        'currency' => 'chf',
+    ],
+
+    // E-Mail Einstellungen (für Onboarding)
+    'mail' => [
+        'host' => 'smtp.example.com',
+        'port' => 587,
+        'username' => '',
+        'password' => '',
+        'from_address' => 'noreply@aurora-livecam.com',
+        'from_name' => 'Aurora Livecam',
+    ],
+
+    // Sicherheit
+    'security' => [
+        'session_lifetime' => 7200, // 2 Stunden
+        'remember_me_days' => 30,
+        'password_min_length' => 8,
+    ],
+];