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.

pyproject.toml

@@ -56,6 +56,7 @@ pty = [
 honcho = ["honcho-ai>=2.0.1"]
 mcp = ["mcp>=1.2.0"]
 homeassistant = ["aiohttp>=3.9.0"]
+sms = ["aiohttp>=3.9.0"]
 acp = ["agent-client-protocol>=0.8.1,<1.0"]
 rl = [
   "atroposlib @ git+https://github.com/NousResearch/atropos.git",
@@ -78,6 +79,7 @@ all = [
   "hermes-agent[honcho]",
   "hermes-agent[mcp]",
   "hermes-agent[homeassistant]",
+  "hermes-agent[sms]",
   "hermes-agent[acp]",
   "hermes-agent[voice]",
 ]