Add global occupied/vacant default templates with per-room overrides

Settings gains a 'Default Templates' section: arrival-prep/departure-prep offsets,
a default aircon template (on/off, mode, setpoint, fan speed x occupied/vacant), and
default TRV setpoints. Every room can individually override any of these fields via
per-field 'Override' toggles in its Schedule modal, falling back to the global
default when not overridden.

Backend:
- zones table: occupied_temp/vacant_temp/heating_offset_min/cooling_offset_min are
  now nullable (NULL = inherit default); existing values preserved as explicit
  per-room overrides, so no room's behaviour changes on deploy. 8 new nullable
  ac_occupied_*/ac_vacant_* override columns.
- New 'hvac_defaults' config key (generic config store) holds the global template.
- scheduler.js: resolves each field as zone-override ?? global-default, and now
  also drives AC state automatically on occupancy transitions (previously AC was
  100% manual) via the same command path the manual control panel uses.
- lib/ac-control.js: factored the mhi_mqtt/mhi_modbus command logic out of
  routes/override.js so the scheduler and the manual control route share one path.
- zones.js PATCH: explicit-null-clears-override semantics for the 12 overridable
  fields (distinct from omitting the key, which leaves the value unchanged).

Frontend:
- Settings.tsx: new Default Templates section matching the requested layout.
- ZoneDetailModal.tsx: per-field Override checkboxes for offsets, AC
  occupied/vacant template, and TRV occupied/vacant setpoints.

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

backend/src/db.js

@@ -23,10 +23,21 @@ export async function initDb() {
       newbook_site_id    TEXT UNIQUE,
       name               TEXT NOT NULL,
       active             BOOLEAN NOT NULL DEFAULT TRUE,     -- soft-deactivate on NewBook sync, never hard delete
-      occupied_temp      NUMERIC(4,1) NOT NULL DEFAULT 22.0,
-      vacant_temp        NUMERIC(4,1) NOT NULL DEFAULT 16.0,
-      heating_offset_min INT NOT NULL DEFAULT 120,          -- minutes before arrival to start heating
-      cooling_offset_min INT NOT NULL DEFAULT -30,          -- minutes after departure to stop (negative = before checkout)
+      -- TRV temps + offsets: NULL = inherit the global 'hvac_defaults' config template (see seedDefaults()).
+      -- A non-NULL value here is an explicit per-room override.
+      occupied_temp      NUMERIC(4,1),
+      vacant_temp        NUMERIC(4,1),
+      heating_offset_min INT,                                -- minutes before arrival to start heating
+      cooling_offset_min INT,                                -- minutes after departure to stop (negative = before checkout)
+      -- Aircon template overrides — same inherit-if-NULL relationship to hvac_defaults.ac_occupied/ac_vacant.
+      ac_occupied_power     TEXT,                             -- 'on' | 'off'
+      ac_occupied_mode      TEXT,                             -- cool | heat | fan | auto | dry
+      ac_occupied_setpoint  NUMERIC(4,1),
+      ac_occupied_fan_speed TEXT,                             -- low | medium | high | powerful
+      ac_vacant_power       TEXT,
+      ac_vacant_mode        TEXT,
+      ac_vacant_setpoint    NUMERIC(4,1),
+      ac_vacant_fan_speed   TEXT,
       auto_mode          BOOLEAN NOT NULL DEFAULT TRUE,
       sync_valves        BOOLEAN NOT NULL DEFAULT TRUE,     -- sync guest setpoint changes across valves in the same zone
       exclude_bathroom   BOOLEAN NOT NULL DEFAULT TRUE,     -- bathroom valve excluded from guest-adjustment sync
@@ -152,9 +163,41 @@ export async function initDb() {
   await pool.query(`ALTER TABLE zone_devices ADD COLUMN IF NOT EXISTS remote_locked BOOLEAN`)
   await pool.query(`ALTER TABLE zone_devices ADD COLUMN IF NOT EXISTS status_updated_at TIMESTAMPTZ`)
 
+  // Default-template rollout: existing installs created occupied_temp/vacant_temp/
+  // heating_offset_min/cooling_offset_min as NOT NULL with a hardcoded default — relax
+  // that so NULL can mean "inherit the global hvac_defaults template" (see seedDefaults()
+  // below). Every existing room's current value is preserved as its explicit override —
+  // nothing changes behaviourally for any room on deploy. DROP NOT NULL/DROP DEFAULT are
+  // no-ops (not errors) if already relaxed, so this stays safe to run on every startup.
+  for (const col of ['occupied_temp', 'vacant_temp', 'heating_offset_min', 'cooling_offset_min']) {
+    await pool.query(`ALTER TABLE zones ALTER COLUMN ${col} DROP NOT NULL`)
+    await pool.query(`ALTER TABLE zones ALTER COLUMN ${col} DROP DEFAULT`)
+  }
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_occupied_power TEXT`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_occupied_mode TEXT`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_occupied_setpoint NUMERIC(4,1)`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_occupied_fan_speed TEXT`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_vacant_power TEXT`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_vacant_mode TEXT`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_vacant_setpoint NUMERIC(4,1)`)
+  await pool.query(`ALTER TABLE zones ADD COLUMN IF NOT EXISTS ac_vacant_fan_speed TEXT`)
+
   await seedDefaults()
 }
 
+// Global fallback template for every room's occupied/vacant TRV + aircon state, used
+// wherever a zone's own override column is NULL. Structured as a single 'hvac_defaults'
+// config value (not a dedicated table) since the generic config store already holds
+// arbitrary JSONB per key — see routes/config.js.
+export const DEFAULT_HVAC_TEMPLATE = {
+  arrival_prep_offset_min:   120,    // minutes before arrival to start heating
+  departure_prep_offset_min: -30,    // minutes after departure to start cooling (negative = before checkout)
+  trv_occupied_temp: 22.0,
+  trv_vacant_temp:   16.0,
+  ac_occupied: { power: 'on',  mode: 'cool', setpoint: 22.0, fan_speed: 'medium' },
+  ac_vacant:   { power: 'off', mode: 'cool', setpoint: 18.0, fan_speed: 'low' },
+}
+
 async function seedDefaults() {
   const defaults = {
     automation_enabled:     true,   // master kill switch — overrides every zone's own auto_mode
@@ -164,6 +207,7 @@ async function seedDefaults() {
     default_departure_time: '10:00:00',
     maintenance_url:        '',
     maintenance_api_key:    '',
+    hvac_defaults:          DEFAULT_HVAC_TEMPLATE,
   }
   for (const [key, value] of Object.entries(defaults)) {
     await pool.query(