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/components/listings/price-history-chart.tsx

@@ -11,21 +11,13 @@ import {
 } from 'recharts';
 
 import type { PriceHistoryItem } from '@/lib/listings-api';
+import { formatPrice } from '@/lib/currency';
 
 interface PriceHistoryChartProps {
   data: PriceHistoryItem[];
   height?: number;
 }
 
-function priceToMillions(priceStr: string): number {
-  return Math.round(Number(priceStr) / 1_000_000);
-}
-
-function formatMillions(value: number): string {
-  if (value >= 1000) return `${(value / 1000).toFixed(1)} tỷ`;
-  return `${value} tr`;
-}
-
 export function PriceHistoryChart({ data, height = 280 }: PriceHistoryChartProps) {
   if (data.length === 0) return null;
 
@@ -37,7 +29,7 @@ export function PriceHistoryChart({ data, height = 280 }: PriceHistoryChartProps
         month: '2-digit',
         year: 'numeric',
       }),
-      price: priceToMillions(item.newPrice),
+      price: Number(item.newPrice),
     }));
 
   return (
@@ -48,7 +40,7 @@ export function PriceHistoryChart({ data, height = 280 }: PriceHistoryChartProps
         <YAxis
           tick={{ fontSize: 11 }}
           className="fill-muted-foreground"
-          tickFormatter={(v: number) => formatMillions(v)}
+          tickFormatter={(v: number) => formatPrice(v)}
         />
         <Tooltip
           contentStyle={{
@@ -57,7 +49,7 @@ export function PriceHistoryChart({ data, height = 280 }: PriceHistoryChartProps
             borderRadius: '0.5rem',
             fontSize: '0.875rem',
           }}
-          formatter={(value) => [formatMillions(Number(value)), 'Giá']}
+          formatter={(value) => [formatPrice(Number(value)), 'Giá']}
         />
         <Line
           type="monotone"