feat: add SMS (Telnyx) platform adapter

Implement SMS as a first-class messaging platform following
ADDING_A_PLATFORM.md checklist. All 16 integration points covered:

- gateway/platforms/sms.py: Core adapter with aiohttp webhook server,
  Telnyx REST API send, markdown stripping, 1600-char chunking,
  echo loop prevention, multi-number reply-from tracking
- gateway/config.py: Platform.SMS enum + env override block
- gateway/run.py: Adapter factory + auth maps (SMS_ALLOWED_USERS,
  SMS_ALLOW_ALL_USERS)
- toolsets.py: hermes-sms toolset + included in hermes-gateway
- cron/scheduler.py: SMS in platform_map for cron delivery
- tools/send_message_tool.py: SMS routing + _send_sms() standalone sender
- tools/cronjob_tools.py: 'sms' in deliver description
- gateway/channel_directory.py: SMS in session-based discovery
- agent/prompt_builder.py: SMS platform hint (plain text, concise)
- hermes_cli/status.py: SMS in platforms status display
- hermes_cli/gateway.py: SMS in setup wizard with Telnyx instructions
- pyproject.toml: sms optional dependency group (aiohttp>=3.9.0)
- tests/gateway/test_sms.py: Unit tests for config, format, truncate,
  echo prevention, requirements, toolset integration

Co-authored-by: sunsakis <teo@sunsakis.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

gateway/config.py

@@ -42,6 +42,7 @@ class Platform(Enum):
     SIGNAL = "signal"
     HOMEASSISTANT = "homeassistant"
     EMAIL = "email"
+    SMS = "sms"
 
 
 @dataclass
@@ -225,6 +226,9 @@ class GatewayConfig:
             # WhatsApp uses enabled flag only (bridge handles auth)
             elif platform == Platform.WHATSAPP:
                 connected.append(platform)
+            # SMS uses api_key from env (checked via extra or env var)
+            elif platform == Platform.SMS and os.getenv("TELNYX_API_KEY"):
+                connected.append(platform)
             # Signal uses extra dict for config (http_url + account)
             elif platform == Platform.SIGNAL and config.extra.get("http_url"):
                 connected.append(platform)
@@ -563,6 +567,21 @@ def _apply_env_overrides(config: GatewayConfig) -> None:
                 name=os.getenv("EMAIL_HOME_ADDRESS_NAME", "Home"),
             )
 
+    # SMS (Telnyx)
+    telnyx_key = os.getenv("TELNYX_API_KEY")
+    if telnyx_key:
+        if Platform.SMS not in config.platforms:
+            config.platforms[Platform.SMS] = PlatformConfig()
+        config.platforms[Platform.SMS].enabled = True
+        config.platforms[Platform.SMS].api_key = telnyx_key
+        sms_home = os.getenv("SMS_HOME_CHANNEL")
+        if sms_home:
+            config.platforms[Platform.SMS].home_channel = HomeChannel(
+                platform=Platform.SMS,
+                chat_id=sms_home,
+                name=os.getenv("SMS_HOME_CHANNEL_NAME", "Home"),
+            )
+
     # Session settings
     idle_minutes = os.getenv("SESSION_IDLE_MINUTES")
     if idle_minutes: