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/app/[locale]/(public)/page.tsx

@@ -17,23 +17,13 @@ import {
   usePriceMovers,
   useTrendingAreas,
 } from '@/lib/hooks/use-analytics';
+import { formatCompact } from '@/lib/currency';
 import { listingsApi, type ListingDetail } from '@/lib/listings-api';
 
 /* ------------------------------------------------------------------ */
 /*  Helpers                                                           */
 /* ------------------------------------------------------------------ */
 
-const vndFmt = new Intl.NumberFormat('vi-VN', {
-  style: 'currency',
-  currency: 'VND',
-  maximumFractionDigits: 0,
-});
-
-function formatVnd(value: number): string {
-  if (value >= 1_000_000_000) return `${(value / 1_000_000_000).toFixed(1)} tỷ`;
-  if (value >= 1_000_000) return `${(value / 1_000_000).toFixed(0)} tr`;
-  return vndFmt.format(value);
-}
 
 function formatPriceM2(value: number): string {
   if (value >= 1_000_000) return `${(value / 1_000_000).toFixed(1)} tr/m²`;
@@ -146,7 +136,7 @@ function KpiStrip({ city }: { city: string }) {
       />
       <KpiCard
         label="Giá TB"
-        value={data ? formatVnd(data.avgPrice) : '—'}
+        value={data ? formatCompact(data.avgPrice) : '—'}
         delta={data?.priceChangePct?.d30}
         footnote="Toàn thành phố"
         icon={<Building2 className="h-3.5 w-3.5" />}
@@ -154,7 +144,7 @@ function KpiStrip({ city }: { city: string }) {
       />
       <KpiCard
         label="Giá trung vị"
-        value={data ? formatVnd(data.medianPrice) : '—'}
+        value={data ? formatCompact(data.medianPrice) : '—'}
         footnote="Median price"
         icon={<Layers className="h-3.5 w-3.5" />}
         loading={isLoading}
@@ -352,7 +342,7 @@ function RecentListings() {
           const price = Number(r.priceVND);
           return (
             <span className="font-mono text-sm font-semibold tabular-nums text-foreground">
-              {formatVnd(price)}
+              {formatCompact(price)}
             </span>
           );
         },