feat: add SMS (Twilio) platform adapter

Add SMS as a first-class messaging platform via the Twilio API.
Shares credentials with the existing telephony skill — same
TWILIO_ACCOUNT_SID, TWILIO_AUTH_TOKEN, TWILIO_PHONE_NUMBER env vars.

Adapter (gateway/platforms/sms.py):
- aiohttp webhook server for inbound (Twilio form-encoded POSTs)
- Twilio REST API with Basic auth for outbound
- Markdown stripping, smart chunking at 1600 chars
- Echo loop prevention, phone number redaction in logs

Integration (13 files):
- gateway config, run, channel_directory
- agent prompt_builder (SMS platform hint)
- cron scheduler, cronjob tools
- send_message_tool (_send_sms via Twilio API)
- toolsets (hermes-sms + hermes-gateway)
- gateway setup wizard, status display
- pyproject.toml (sms optional extra)
- 21 tests

Docs:
- website/docs/user-guide/messaging/sms.md (full setup guide)
- Updated messaging index (architecture, toolsets, security, links)
- Updated environment-variables.md reference

Inspired by PR #1575 (@sunsakis), rewritten for Twilio.

website/docs/reference/environment-variables.md

@@ -152,6 +152,14 @@ For native Anthropic auth, Hermes prefers Claude Code's own credential files whe
 | `SIGNAL_HOME_CHANNEL_NAME` | Display name for the Signal home channel |
 | `SIGNAL_IGNORE_STORIES` | Ignore Signal stories/status updates |
 | `SIGNAL_ALLOW_ALL_USERS` | Allow all Signal users without an allowlist |
+| `TWILIO_ACCOUNT_SID` | Twilio Account SID (shared with telephony skill) |
+| `TWILIO_AUTH_TOKEN` | Twilio Auth Token (shared with telephony skill) |
+| `TWILIO_PHONE_NUMBER` | Twilio phone number in E.164 format (shared with telephony skill) |
+| `SMS_WEBHOOK_PORT` | Webhook listener port for inbound SMS (default: `8080`) |
+| `SMS_ALLOWED_USERS` | Comma-separated E.164 phone numbers allowed to chat |
+| `SMS_ALLOW_ALL_USERS` | Allow all SMS senders without an allowlist |
+| `SMS_HOME_CHANNEL` | Phone number for cron job / notification delivery |
+| `SMS_HOME_CHANNEL_NAME` | Display name for the SMS home channel |
 | `EMAIL_ADDRESS` | Email address for the Email gateway adapter |
 | `EMAIL_PASSWORD` | Password or app password for the email account |
 | `EMAIL_IMAP_HOST` | IMAP hostname for the email adapter |