feat(cli): add alerts command for scriptable alarm-state scans

[jongio]

What

Adds a one-shot thermoworks alerts command that scans the current alarm state across your devices and reports any channel that is actively alarming. Without a serial it checks every device on the account; pass a serial to scope to one device.

npx thermoworks alerts           # all devices
npx thermoworks alerts <serial>  # one device
npx thermoworks alerts --json    # machine-readable

# fire a notification when anything is alarming
npx thermoworks alerts || notify-send "ThermoWorks alarm"

Why

The CLI can arm and list alarms (alarm set / alarm list), but there was no scriptable way to ask "is anything alarming right now?" watch shows live alarm state on screen, but you cannot drop it in a cron job or shell loop. alerts fills that gap with a plain exit-code contract.

How

• Reuses the SDK getChannelAlarmState helper to classify each channel as high, low, or none.
• Scans with getDevices / getDevice plus getAllDeviceChannels. Read-only, so it never writes to a device.
• Exits 1 when at least one channel is alarming and 0 when everything is clear. The exit code is set in both human and --json modes so scripts can branch on it.
• Human output groups alarming channels under a bold device header; --json prints an array of { serial, deviceLabel, channel, channelLabel, state, value, units }.

Testing

• Added packages/cli/tests/alerts.test.ts: high and low alarm detection with a non-zero exit code, the clear case at exit 0, single-device scoping via getDevice, JSON output shape, empty JSON array, and the not-logged-in error path.
• pnpm --dir packages/cli typecheck clean.
• pnpm --dir packages/cli test green (883 tests).
• pnpm lint clean.

Docs

• packages/cli/README.md: new thermoworks alerts section.
• docs/cli-reference.md: new thermoworks alerts reference plus added to the --json supported-commands list.

Closes #276