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.

toolsets.py

@@ -292,10 +292,16 @@ TOOLSETS = {
         "includes": []
     },
 
+    "hermes-sms": {
+        "description": "SMS bot toolset - interact with Hermes via SMS (Twilio)",
+        "tools": _HERMES_CORE_TOOLS,
+        "includes": []
+    },
+
     "hermes-gateway": {
         "description": "Gateway toolset - union of all messaging platform tools",
         "tools": [],
-        "includes": ["hermes-telegram", "hermes-discord", "hermes-whatsapp", "hermes-slack", "hermes-signal", "hermes-homeassistant", "hermes-email"]
+        "includes": ["hermes-telegram", "hermes-discord", "hermes-whatsapp", "hermes-slack", "hermes-signal", "hermes-homeassistant", "hermes-email", "hermes-sms"]
     }
 }