Add MHI aircon manual control (Phase 2, Modbus only)

Manual on/off/mode/setpoint/fan control for MHI indoor units via the
already-verified Intesis Modbus TCP gateway, deliberately NOT wired into
the NewBook-driven scheduler yet — that stays deferred. Modbus doesn't
depend on the MQTT broker (separate infra, still unbuilt), so this can be
deployed and tested standalone.

- mhi_gateways table (connection config: host/port/slave id/address base)
  + zone_devices columns for MHI devices (gateway id, unit index, IU hint,
  and the per-device register map staged from a MAPS import — ground
  truth, never re-derived from room/IU at runtime)
- drivers/mhi-modbus.js: discover/getStatus/setTarget over modbus-serial,
  same interface as trv.js/homeassistant.js; per-gateway request queue
  since Modbus TCP requires serialised requests; falls back to the
  profile's stride formula (with a loud warning) only if a unit has never
  been through an import
- routes/mhi-gateways.js: gateway CRUD, live test-connection, xlsx import
  (stages the parsed result for review — never auto-creates devices),
  per-unit 'assign to zone' as the explicit commit step
- routes/override.js: GET .../mhi-status, POST .../mhi-control (control cap)
- frontend: GatewaysPanel (add gateway, test connection, import + preview,
  assign units) and MhiControlPanel (on/off, mode, setpoint, fan) wired
  into Devices.tsx / ZoneDetailModal.tsx

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/components/MhiControlPanel.tsx

@@ -0,0 +1,102 @@
+import { useEffect, useState } from 'react'
+import { Power, Minus, Plus, RefreshCw, Loader2 } from 'lucide-react'
+import { MHI_MODES, MHI_FAN_SPEEDS } from '../types'
+import { fetchMhiStatus, sendMhiControl } from '../api'
+
+// Manual on/off + mode + setpoint + fan speed controls for one assigned MHI
+// aircon unit (mhi_modbus). No NewBook/scheduler integration — every change
+// here is an explicit staff action via POST /devices/:id/mhi-control.
+export default function MhiControlPanel({ deviceId, canControl }: { deviceId: number; canControl: boolean }) {
+  const [loading, setLoading] = useState(true)
+  const [error, setError] = useState('')
+  const [applying, setApplying] = useState(false)
+
+  const [onOff, setOnOff] = useState(false)
+  const [mode, setMode] = useState<string>('auto')
+  const [setpoint, setSetpoint] = useState(21)
+  const [fanSpeed, setFanSpeed] = useState<string>('medium')
+  const [roomTemp, setRoomTemp] = useState<number | null>(null)
+
+  function load() {
+    setLoading(true); setError('')
+    fetchMhiStatus(deviceId)
+      .then(s => {
+        setOnOff(s.onOff === 'on')
+        if (s.mode) setMode(s.mode)
+        if (s.setpoint != null) setSetpoint(s.setpoint)
+        if (s.fanSpeed) setFanSpeed(s.fanSpeed)
+        setRoomTemp(s.roomTemp ?? null)
+      })
+      .catch(e => setError(e instanceof Error ? e.message : 'Failed to read device status'))
+      .finally(() => setLoading(false))
+  }
+  useEffect(load, [deviceId])
+
+  async function apply(patch: Partial<{ onOff: boolean; mode: string; tempC: number; fanSpeed: string }>) {
+    setApplying(true); setError('')
+    try {
+      const res = await sendMhiControl(deviceId, patch)
+      if (!res.ok) setError('Device did not accept the command')
+    } catch (e) {
+      setError(e instanceof Error ? e.message : 'Command failed')
+    } finally {
+      setApplying(false)
+    }
+  }
+
+  if (loading) return <p className="muted" style={{ fontSize: 12.5 }}>Reading aircon status…</p>
+
+  return (
+    <div style={{ marginTop: 8 }}>
+      {error && <div className="error-banner" style={{ marginBottom: 8 }}>{error}</div>}
+      <div style={{ display: 'flex', alignItems: 'center', gap: 10, flexWrap: 'wrap' }}>
+        <button
+          className="btn btn-sm"
+          disabled={!canControl || applying}
+          onClick={() => { const next = !onOff; setOnOff(next); apply({ onOff: next }) }}
+          style={onOff ? { background: 'var(--gold)', borderColor: 'var(--gold)', color: 'var(--navy)' } : undefined}
+        >
+          <Power size={13} strokeWidth={1.75} /> {onOff ? 'On' : 'Off'}
+        </button>
+
+        <select
+          disabled={!canControl || applying}
+          value={mode}
+          onChange={e => { setMode(e.target.value); apply({ mode: e.target.value }) }}
+        >
+          {MHI_MODES.map(m => <option key={m} value={m}>{m[0].toUpperCase() + m.slice(1)}</option>)}
+        </select>
+
+        <div style={{ display: 'flex', alignItems: 'center', gap: 4 }}>
+          <button
+            className="btn btn-sm" disabled={!canControl || applying}
+            onClick={() => { const next = Math.max(16, setpoint - 0.5); setSetpoint(next); apply({ tempC: next }) }}
+          >
+            <Minus size={12} strokeWidth={1.75} />
+          </button>
+          <span style={{ minWidth: 48, textAlign: 'center', fontWeight: 600, fontSize: 13 }}>{setpoint.toFixed(1)}°C</span>
+          <button
+            className="btn btn-sm" disabled={!canControl || applying}
+            onClick={() => { const next = Math.min(30, setpoint + 0.5); setSetpoint(next); apply({ tempC: next }) }}
+          >
+            <Plus size={12} strokeWidth={1.75} />
+          </button>
+        </div>
+
+        <select
+          disabled={!canControl || applying}
+          value={fanSpeed}
+          onChange={e => { setFanSpeed(e.target.value); apply({ fanSpeed: e.target.value }) }}
+        >
+          {MHI_FAN_SPEEDS.map(f => <option key={f} value={f}>{f[0].toUpperCase() + f.slice(1)}</option>)}
+        </select>
+
+        {roomTemp != null && <span className="muted" style={{ fontSize: 12 }}>Room: {roomTemp.toFixed(1)}°C</span>}
+
+        <button className="btn btn-sm" disabled={loading} onClick={load} title="Refresh live status">
+          {applying ? <Loader2 size={13} strokeWidth={1.75} className="spin" /> : <RefreshCw size={13} strokeWidth={1.75} />}
+        </button>
+      </div>
+    </div>
+  )
+}