feat(sms): implement SMS messaging and metered billing

Implement a complete SMS messaging system including:
- Integration with SMS Manager.cz API for sending messages.
- Metered billing via Stripe using monthly aggregate invoice items.
- Backend services for managing SMS settings, usage logging, and monthly reporting.
- Database migrations for tenant settings, usage logs, and monthly reports.
- Frontend dashboard components for SMS configuration, usage tracking, and history.
- Support for customer phone numbers in the booking flow.

Includes new migrations, backend services, and frontend UI components.

.env.example

@@ -26,6 +26,19 @@ BOOKRA_STRIPE_PRO_USD_YEARLY_PRICE_ID=price_1TVAnjGrjyNQaOSGvAANw64k
 BOOKRA_STRIPE_BUSINESS_CZK_YEARLY_PRICE_ID=price_1TVAmsGrjyNQaOSGL7Sl5cCd
 BOOKRA_STRIPE_BUSINESS_USD_YEARLY_PRICE_ID=price_1TVAo7GrjyNQaOSGB8LSCOua
 
+# Stripe SMS prices — one per market/currency (create as standard prices, not metered)
+# These are used for monthly aggregate billing (invoice item at month end)
+# Czech: 1.50 CZK per SMS | US: ~$0.065 per SMS | EUR: ~€0.060 | GBP: ~£0.050 | PLN: ~0.27zł
+BOOKRA_STRIPE_SMS_CZK_PRICE_ID=price_xxx
+BOOKRA_STRIPE_SMS_USD_PRICE_ID=price_xxx
+BOOKRA_STRIPE_SMS_EUR_PRICE_ID=
+BOOKRA_STRIPE_SMS_GBP_PRICE_ID=
+BOOKRA_STRIPE_SMS_PLN_PRICE_ID=
+
+# SMS Manager.cz API (optional - SMS feature)
+BOOKRA_SMSMANAGER_API_KEY=your_smsmanager_api_key
+BOOKRA_SMSMANAGER_BASE_URL=https://api.smsmngr.com/v2
+
 # Legacy price IDs (fallback)
 BOOKRA_STRIPE_STARTER_CZK_PRICE_ID=price_1TV6Z6GrjyNQaOSGZFcmltqI
 BOOKRA_STRIPE_STARTER_USD_PRICE_ID=price_1TV6cAGrjyNQaOSGXBhOq3Dk