fix(gateway): persist /sethome home channel to .env across all platforms

_handle_set_home_command wrote FEISHU_HOME_CHANNEL / DISCORD_HOME_CHANNEL /
etc. as top-level keys into config.yaml, but load_gateway_config() only
reads home channels from env vars. After every gateway restart the home
channel was lost — on every platform, not just Feishu.

Fix: switch /sethome to save_env_value(), which atomically writes to
~/.hermes/.env and updates the current process env in one shot. The
handler builds the env key from platform_name.upper(), so one line
change repairs /sethome for every platform that has a HOME_CHANNEL
env var.

Also widen _EXTRA_ENV_KEYS in hermes_cli/config.py so HOME_CHANNEL and
HOME_CHANNEL_NAME for every platform are treated as managed env vars:
SIGNAL, SLACK, SMS, DINGTALK, BLUEBUBBLES, FEISHU, WECOM, YUANBAO, plus
the missing *_NAME variants for DISCORD/TELEGRAM/MATTERMOST.

Closes #16806

Co-authored-by: teknium1 <screenmachine@gmail.com>

gateway/run.py

@@ -6384,18 +6384,10 @@ class GatewayRunner:
         
         env_key = f"{platform_name.upper()}_HOME_CHANNEL"
         
-        # Save to config.yaml
+        # Save to .env so it persists across restarts
         try:
-            import yaml
-            config_path = _hermes_home / 'config.yaml'
-            user_config = {}
-            if config_path.exists():
-                with open(config_path, encoding="utf-8") as f:
-                    user_config = yaml.safe_load(f) or {}
-            user_config[env_key] = chat_id
-            atomic_yaml_write(config_path, user_config)
-            # Also set in the current environment so it takes effect immediately
-            os.environ[env_key] = str(chat_id)
+            from hermes_cli.config import save_env_value
+            save_env_value(env_key, str(chat_id))
         except Exception as e:
             return f"Failed to save home channel: {e}"