When shutil.which('hermes') returns None, _resolve_hermes_bin() now tries
sys.executable -m hermes_cli.main as a fallback. This handles setups where
Hermes is launched via a venv or module invocation and the hermes symlink is
not on PATH for the gateway process.
Fixes#1049
Adds a /update command to Telegram, Discord, and other gateway platforms
that runs `hermes update` to pull the latest code, update dependencies,
sync skills, and restart the gateway.
Implementation:
- Spawns `hermes update` in a separate systemd scope (systemd-run --user
--scope) so the process survives the gateway restart that hermes update
triggers at the end. Falls back to nohup if systemd-run is unavailable.
- Writes a marker file (.update_pending.json) with the originating
platform and chat_id before spawning the update.
- On gateway startup, _send_update_notification() checks for the marker,
reads the captured update output, sends the results back to the user,
and cleans up.
Also:
- Registers /update as a Discord slash command
- Updates README.md, docs/messaging.md, docs/slash-commands.md
- Adds 18 tests covering handler, notification, and edge cases
