feat(gro-194): SMS provider service with Telnyx SDK integration

- Added telnyx npm package
- Created sms.ts with SmsProvider interface
- Implemented TelnyxProvider with sendSms() and validateWebhookSignature()
- Added createSmsProvider() factory function
- Added smsSend() convenience function that skips when SMS_ENABLED=false
- Provider abstraction allows future Twilio or other providers
- E.164 phone validation on send
- Webhook signature verification using HMAC-SHA256

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/api/package.json

@@ -22,6 +22,7 @@
     "hono": "^4.6.17",
     "node-cron": "^3.0.3",
     "nodemailer": "^6.9.16",
+    "telnyx": "^6.41.0",
     "zod": "^4.3.6"
   },
   "devDependencies": {