Adds Twilio SMS as a new notification channel, allowing users to
receive SMS alerts via the Twilio API.
Backend: provider using HTTP Basic Auth, type registration, validation,
service wiring. Uses existing fields: address (Account SID),
accessToken (Auth Token), homeserverUrl (From number), phone (To number).
Frontend: form UI with 4 fields, validation, i18n keys.
Tests: 18 provider tests + updated service test constructor.
Closes#3095
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>