fix(web): consolidate inline currency formatters into shared lib (GOO-205)

Remove 8 inline formatPrice/formatVND/formatPriceM2 functions scattered
across components and pages, replacing them with imports from
@/lib/currency. Add formatVNDFull (full locale, no compact notation) for
chuyen-nhuong pages. Fix price-history-chart off-by-1000 bug caused by
double-dividing through priceToMillions then formatMillions. Add k/m²
branch to formatPricePerM2 for sub-million values.

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

apps/web/app/[locale]/(dashboard)/dashboard/saved-searches/page.tsx

@@ -10,6 +10,7 @@ import {
   useUpdateSavedSearch,
 } from '@/lib/hooks/use-saved-searches';
 import { type SavedSearch, type SavedSearchFilters } from '@/lib/saved-search-api';
+import { formatPrice } from '@/lib/currency';
 
 const PROPERTY_TYPE_LABELS: Record<string, string> = {
   APARTMENT: 'Chung cư',
@@ -25,12 +26,6 @@ const TRANSACTION_TYPE_LABELS: Record<string, string> = {
   RENT: 'Cho thuê',
 };
 
-function formatPrice(value: string): string {
-  const num = Number(value);
-  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)} triệu`;
-  return num.toLocaleString('vi-VN');
-}
 
 function formatFilters(filters: SavedSearchFilters): string[] {
   const parts: string[] = [];

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

@@ -18,27 +18,12 @@ import {
   useTrendingAreas,
 } from '@/lib/hooks/use-analytics';
 import { listingsApi, type ListingDetail } from '@/lib/listings-api';
+import { formatPrice, formatPricePerM2 } from '@/lib/currency';
 
 /* ------------------------------------------------------------------ */
 /*  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 `${(value / 1_000_000).toFixed(1)} tr/m²`;
-  return `${Math.round(value / 1000)}k/m²`;
-}
 
 function currentPeriod(): string {
   const now = new Date();
@@ -138,7 +123,7 @@ function KpiStrip({ city }: { city: string }) {
     <section className="mb-6 grid grid-cols-2 gap-3 md:grid-cols-4">
       <KpiCard
         label="GGI HCM"
-        value={data ? formatPriceM2(data.avgPricePerM2) : '—'}
+        value={data ? formatPricePerM2(data.avgPricePerM2) : '—'}
         delta={data?.priceChangePct?.d7}
         footnote="Chỉ số giá TB/m²"
         icon={<BarChart3 className="h-3.5 w-3.5" />}
@@ -146,7 +131,7 @@ function KpiStrip({ city }: { city: string }) {
       />
       <KpiCard
         label="Giá TB"
-        value={data ? formatVnd(data.avgPrice) : '—'}
+        value={data ? formatPrice(data.avgPrice) : '—'}
         delta={data?.priceChangePct?.d30}
         footnote="Toàn thành phố"
         icon={<Building2 className="h-3.5 w-3.5" />}
@@ -154,7 +139,7 @@ function KpiStrip({ city }: { city: string }) {
       />
       <KpiCard
         label="Giá trung vị"
-        value={data ? formatVnd(data.medianPrice) : '—'}
+        value={data ? formatPrice(data.medianPrice) : '—'}
         footnote="Median price"
         icon={<Layers className="h-3.5 w-3.5" />}
         loading={isLoading}
@@ -352,7 +337,7 @@ function RecentListings() {
           const price = Number(r.priceVND);
           return (
             <span className="font-mono text-sm font-semibold tabular-nums text-foreground">
-              {formatVnd(price)}
+              {formatPrice(price)}
             </span>
           );
         },
@@ -367,7 +352,7 @@ function RecentListings() {
         cell: (r) =>
           r.pricePerM2 ? (
             <span className="text-xs tabular-nums text-foreground-muted">
-              {formatPriceM2(r.pricePerM2)}
+              {formatPricePerM2(r.pricePerM2)}
             </span>
           ) : (
             <span className="text-foreground-dim">—</span>
@@ -457,7 +442,7 @@ export default function MarketDashboardPage() {
       {
         id: 'price',
         header: 'Giá TB/m²',
-        cell: (r) => formatPriceM2(r.avgPriceM2),
+        cell: (r) => formatPricePerM2(r.avgPriceM2),
         align: 'right' as const,
         numeric: true,
         sortable: true,