Add Daikin local-API driver — MAC-matched subnet sweep instead of UDP broadcast

Daikin BRP069/BRP072-class units are WiFi/DHCP with no fixed IP. hvac's backend
runs as a Docker container on its own bridge network (not directly on the LXC's
admin-VLAN NIC), so UDP broadcast discovery risked silently failing to egress —
instead, every unit is identified by MAC (external_ref), and a background poller
periodically HTTP-sweeps the configured subnet CIDR and matches replies by MAC,
self-healing zone_devices.device_ip whenever a lease changes. Only needs plain
outbound HTTP, same path already proven by the MHI Modbus TCP driver.

- lib/drivers/daikin.js: discover()/getStatus()/setTarget() against the local
  /common/basic_info + /aircon/get_control_info + /aircon/set_control_info API
  (confirmed live against firmware 4_2_303, 2026-08-25). Mode/fan-rate encoding
  taken from community reverse-engineering, not yet verified against a live
  setTarget() call — flagged in comments for first real control test.
- lib/daikin-poller.js: 60s status poll (cached IP) + 5min subnet resweep
  (self-heal IP + auto-register new units, never auto-assigned to a zone).
- lib/device-registry.js: shared discover-upsert, extracted so both the manual
  Discover button and the background sweep record device_ip the same way.
- ac-control.js / routes/override.js: daikin-status/daikin-control endpoints
  and commandAcDevice() branch, mirroring the existing MHI control path.
- Settings page: new "Daikin subnet (CIDR)" field (daikin_subnet_cidr config
  key) — sweeps do nothing until this is set.
- Frontend: DaikinControlPanel.tsx (on/off/mode/setpoint/fan), wired into
  ZoneDetailModal; daikin moved from NOT_YET_IMPLEMENTED to a real driver.

Backend node --check and frontend tsc --noEmit both clean.

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

frontend/src/pages/Settings.tsx

@@ -23,6 +23,7 @@ export default function Settings() {
   const [defaultDeparture, setDefaultDeparture] = useState('10:00:00')
   const [maintUrl, setMaintUrl] = useState('')
   const [maintKey, setMaintKey] = useState('')
+  const [daikinCidr, setDaikinCidr] = useState('')
   const [configSaving, setConfigSaving] = useState(false)
 
   // Default occupied/vacant templates — every room inherits these unless it sets its
@@ -57,6 +58,7 @@ export default function Settings() {
       setDefaultDeparture(cfg.default_departure_time ?? '10:00:00')
       setMaintUrl(cfg.maintenance_url ?? '')
       setMaintKey(cfg.maintenance_api_key ?? '')
+      setDaikinCidr(cfg.daikin_subnet_cidr ?? '')
       // Merge onto the shipped default rather than replacing outright — an hvac_defaults
       // row saved before weather compensation existed won't have ac_occupied_tiers yet.
       setDefaults({ ...DEFAULT_HVAC_TEMPLATE, ...cfg.hvac_defaults, ac_occupied_tiers: cfg.hvac_defaults?.ac_occupied_tiers ?? DEFAULT_HVAC_TEMPLATE.ac_occupied_tiers })
@@ -130,6 +132,7 @@ export default function Settings() {
         updateConfig('default_departure_time', defaultDeparture),
         updateConfig('maintenance_url', maintUrl),
         updateConfig('maintenance_api_key', maintKey),
+        updateConfig('daikin_subnet_cidr', daikinCidr),
       ])
       setMsg('Settings saved'); setTimeout(() => setMsg(''), 2500)
     } catch (e) {
@@ -425,6 +428,20 @@ export default function Settings() {
         </button>
       </div>
 
+      <div className="section-title">Daikin Aircon</div>
+      <p className="field-hint" style={{ marginBottom: 10 }}>
+        Daikin units are WiFi/DHCP, so their IP changes over time. Instead of a fixed IP, hvac
+        periodically sweeps this LAN range over HTTP and matches units by their MAC address —
+        set it once and it self-heals if a unit's IP changes. Run "Discover Daikin Split" on the
+        Devices page after saving to find units for the first time.
+      </p>
+      <div className="field-row">
+        <div className="field">
+          <label>Daikin subnet (CIDR)</label>
+          <input type="text" value={daikinCidr} onChange={e => setDaikinCidr(e.target.value)} placeholder="10.4.0.0/22" />
+        </div>
+      </div>
+
       <div className="section-title">Maintenance Integration</div>
       <p className="field-hint" style={{ marginBottom: 10 }}>
         Not yet available — maintenance needs its own Settings → API Keys page first.