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/.gitignore

@@ -0,0 +1,26 @@
+# Configuration (contains secrets)
+config.php
+
+# Cache files
+weather_cache.json
+active_viewers.json
+
+# IDE
+.idea/
+.vscode/
+*.swp
+*.swo
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Logs
+*.log
+logs/
+
+# Vendor (if using composer)
+# vendor/
+
+# Uploads (user content)
+uploads/