Exclude sub-meters from category subtotals in Estimates/Reports/internal API

Water Softener is configured as a submeter (parent_meter_id) of Main Hotel
Water, but estimates.js, reports.js, and internal.js's cost + estimate
routes summed every active meter flatly regardless of parent/child, double-
counting the softener's consumption on top of the main meter's own reading.

Sub-meter rows are still shown individually (useful for diagnostics), just
excluded from the category subtotal/total sums, with a 'submeter' badge on
the row explaining why. Fixes the water figures on Estimates, Reports, and
downstream consumers of internal.js (Directors report, Weekly Actuals).

frontend/src/pages/Estimates.tsx

@@ -6,8 +6,12 @@ import * as api from '../api'
 
 const WINDOW_OPTIONS = [7, 14, 30]
 
+// Sub-meters (parent_meter_id set) project a subset of their parent's own
+// consumption (e.g. the water softener sits inline on the main supply) — their
+// row is still shown for visibility, but excluding them here avoids the
+// subtotal double-counting water/energy that's already in the parent's figure.
 function sumEstimateCosts(rows: EstimateRow[]) {
-  return rows.reduce((acc, r) => ({
+  return rows.filter(r => !r.parent_meter_id).reduce((acc, r) => ({
     projected_consumption: acc.projected_consumption + (r.projected_consumption || 0),
     total_pence: acc.total_pence + r.total_pence,
   }), { projected_consumption: 0, total_pence: 0 })
@@ -104,7 +108,14 @@ export default function Estimates() {
                       <Fragment key={group.category_id}>
                         {group.rows.map(m => (
                           <tr key={m.meter_id}>
-                            <td>{m.meter_name}</td>
+                            <td>
+                              {m.meter_name}
+                              {m.parent_meter_id && (
+                                <span className="badge" style={{ marginLeft: 6 }} title="Sub-meter — reads a subset of its parent meter, excluded from the subtotal below to avoid double-counting">
+                                  submeter
+                                </span>
+                              )}
+                            </td>
                             <td className="num">{m.trailing_window_days}d</td>
                             <td className="num">{m.daily_rate != null ? formatUnits(m.daily_rate, `${m.unit_label}/day`) : '—'}</td>
                             <td className="num">{formatUnits(m.actual_to_date, m.unit_label)}</td>

frontend/src/pages/Reports.tsx

@@ -8,8 +8,12 @@ function extrasFor(m: { ccl_cost_pence: number; rab_levy_cost_pence: number; met
   return m.ccl_cost_pence + m.rab_levy_cost_pence + m.metering_cost_pence + m.other_charges_cost_pence
 }
 
+// Sub-meters (parent_meter_id set) read a subset of their parent's own
+// reading (e.g. the water softener sits inline on the main supply) — their
+// row is still shown for visibility, but excluding them here avoids the
+// subtotal double-counting water/energy that's already in the parent's figure.
 function sumMeterCosts(rows: MeterCostRow[]) {
-  return rows.reduce((acc, r) => ({
+  return rows.filter(r => !r.parent_meter_id).reduce((acc, r) => ({
     consumption: acc.consumption + (r.consumption || 0),
     usage_cost_pence: acc.usage_cost_pence + r.usage_cost_pence,
     standing_cost_pence: acc.standing_cost_pence + r.standing_cost_pence,
@@ -97,6 +101,11 @@ export default function Reports() {
                           <tr key={m.meter_id}>
                             <td>
                               {m.meter_name}
+                              {m.parent_meter_id && (
+                                <span className="badge" style={{ marginLeft: 6 }} title="Sub-meter — reads a subset of its parent meter, excluded from the subtotal below to avoid double-counting">
+                                  submeter
+                                </span>
+                              )}
                               {m.rate_changed_mid_period && (
                                 <span className="badge badge-tou" style={{ marginLeft: 6 }} title={m.segments.map(s => `${s.tariff_name}: ${s.seg_start} – ${s.seg_end}`).join(', ')}>
                                   rate changed

frontend/src/types.ts

@@ -180,6 +180,7 @@ export type ConsumptionBasis = 'no_data' | 'partial' | 'complete' | 'distributed
 export interface MeterCostRow extends CostBreakdown {
   meter_id: number
   meter_name: string
+  parent_meter_id: number | null
   category_id: number
   category_name: string
   unit_label: string
@@ -260,6 +261,7 @@ export interface RollupReport {
 export interface EstimateRow extends CostBreakdown {
   meter_id: number
   meter_name: string
+  parent_meter_id: number | null
   category_id: number
   category_name: string
   unit_label: string