refactor(web): dedup tỷ/triệu compact formatters (GOO-206)

- Add `formatCompact` as an exported alias for `formatPrice` in lib/currency.ts
- Replace 5 inline copies of the tỷ/triệu compact formatter:
  - components/map/listing-map.tsx (local `formatPrice` fn)
  - components/agents/agent-profile-client.tsx (local `fmtVND` fn)
  - app/(dashboard)/dashboard/saved-searches/page.tsx (local `formatPrice` fn)
  - app/(public)/page.tsx (local `formatVnd` fn + `vndFmt` Intl instance)
  - components/listings/price-history-chart.tsx (local `formatMillions` + `priceToMillions`)

All call sites now import from the canonical lib/currency module.
PriceHistoryChart now stores raw VND in chart data (was: millions) so
formatCompact emits correct tỷ/triệu labels using canonical thresholds.

Pre-existing test failures in inquiry/lead/AVM specs are unrelated to this change.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/components/map/listing-map.tsx

@@ -5,16 +5,10 @@ import mapboxgl from 'mapbox-gl';
 import * as React from 'react';
 import 'mapbox-gl/dist/mapbox-gl.css';
 import { ComponentErrorBoundary } from '@/components/error-boundary';
+import { formatCompact } from '@/lib/currency';
 import type { ListingDetail } from '@/lib/listings-api';
 import { useMapboxStyle } from '@/lib/mapbox-style';
 
-function formatPrice(priceVND: string): string {
-  const num = Number(priceVND);
-  if (num >= 1_000_000_000) return `${(num / 1_000_000_000).toFixed(1)} tỷ`;
-  if (num >= 1_000_000) return `${(num / 1_000_000).toFixed(0)} tr`;
-  return num.toLocaleString('vi-VN');
-}
-
 interface ListingMapProps {
   listings: ListingDetail[];
   onMarkerClick?: (listing: ListingDetail) => void;
@@ -67,7 +61,7 @@ function buildGeoJSON(
       geometry: { type: 'Point', coordinates: [lng, lat] },
       properties: {
         id: listing.id,
-        price: formatPrice(listing.priceVND),
+        price: formatCompact(listing.priceVND),
         title: listing.property.title,
         district: listing.property.district ?? '',
         city: listing.property.city ?? '',
@@ -100,7 +94,7 @@ function buildPopupContent(listing: ListingDetail): HTMLDivElement {
   const price = document.createElement('p');
   price.style.cssText =
     'font-weight:700;color:hsl(var(--primary));font-size:14px;margin:0 0 4px;';
-  price.textContent = `${formatPrice(listing.priceVND)} VND`;
+  price.textContent = `${formatCompact(listing.priceVND)} VND`;
   container.appendChild(price);
 
   const title = document.createElement('p');