Add per-TRV control panel + valve/wifi telemetry, restyle dashboard radiator icon

Backend:
- New valve_position column, populated from shellies/<id>/info alongside
  wifi_rssi (was already a column, never actually written to).
- New GET/POST /api/devices/:id/trv-status and /trv-control routes, mirroring
  the mhi-status/mhi-control and daikin-status/daikin-control pattern. Control
  goes through the existing setTargetWithRetry() reliability pipeline.

Frontend:
- New TrvControlPanel.tsx: +/- setpoint control debounced 1s after the last
  click before firing a command (these are battery/deep-sleep valves going
  through a real retry/backoff pipeline, not a cheap register write like MHI/
  Daikin), plus room temp, valve position %, wifi signal, and a live "time
  since last update" readout. Wired into ZoneDetailModal for shelly_trv rows.
- ZoneCard dashboard tile: radiator icon now just shows red when heating_active
  (valve open) / grey when idle, with only the target setpoint alongside it
  (dropped the room-temp half, redundant with the zone-level temp line above).

backend/src/routes/override.js

@@ -1,6 +1,6 @@
 import { requireAuth, requireCap } from '../auth.js'
 import { pool, logActivity } from '../db.js'
-import { batchSetZoneTemperature } from '../lib/mqtt.js'
+import { batchSetZoneTemperature, setTargetWithRetry } from '../lib/mqtt.js'
 import { commandAcDevice } from '../lib/ac-control.js'
 import * as mhiDriver from '../lib/drivers/mhi-modbus.js'
 
@@ -140,4 +140,55 @@ export async function overrideRoutes(app) {
 
     return { ok }
   })
+
+  // GET /api/devices/:id/trv-status — live status for one assigned Shelly TRV, served
+  // from the push-populated cache (mqtt.js keeps current_target_temp/current_room_temp/
+  // battery_pct fresh from shellies/+/status, valve_position/wifi_rssi from
+  // shellies/+/info) — same "read the row, don't round-trip" shape as mhi_mqtt/daikin.
+  app.get('/api/devices/:id/trv-status', { preHandler: requireCap('view') }, async (req, reply) => {
+    const { rows } = await pool.query(
+      `SELECT * FROM zone_devices WHERE id = $1 AND device_type = 'shelly_trv'`,
+      [req.params.id]
+    )
+    if (!rows.length) return reply.status(404).send({ error: 'TRV not found' })
+    const device = rows[0]
+
+    return {
+      external_ref: device.external_ref,
+      setpoint: device.current_target_temp != null ? Number(device.current_target_temp) : undefined,
+      roomTemp: device.current_room_temp != null ? Number(device.current_room_temp) : undefined,
+      heatingActive: device.heating_active,
+      valvePosition: device.valve_position,
+      wifiRssi: device.wifi_rssi,
+      batteryPct: device.battery_pct,
+      targetOrigin: device.target_origin,
+      lastSeen: device.last_seen,
+      statusUpdatedAt: device.status_updated_at,
+    }
+  })
+
+  // POST /api/devices/:id/trv-control — explicit staff setpoint change from the room
+  // modal's TrvControlPanel. Body: { tempC }. Goes through setTargetWithRetry() for the
+  // full reliability pipeline (30s->30min backoff, HTTP wake-up fallback) — same
+  // function the zone-level /override route above uses per-device, just for one TRV.
+  app.post('/api/devices/:id/trv-control', { preHandler: requireCap('control') }, async (req, reply) => {
+    const { rows } = await pool.query(
+      `SELECT * FROM zone_devices WHERE id = $1 AND device_type = 'shelly_trv'`,
+      [req.params.id]
+    )
+    if (!rows.length) return reply.status(404).send({ error: 'TRV not found' })
+    const device = rows[0]
+    const tempC = Number(req.body?.tempC)
+    if (!Number.isFinite(tempC)) return reply.status(400).send({ error: 'tempC must be a number' })
+
+    const ok = await setTargetWithRetry({ external_ref: device.external_ref, device_ip: device.device_ip }, tempC)
+
+    await logActivity(device.zone_id, 'device_command', {
+      note: `TRV manual setpoint on ${device.location || device.discovered_name || device.external_ref}: ${tempC}°C${ok ? '' : ' — FAILED'}`,
+      source: 'manual',
+      userEmail: req.user.email,
+    })
+
+    return { ok }
+  })
 }