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/lib/currency.ts

@@ -97,6 +97,18 @@ export function formatPricePerM2(price: string | number): string {
   return `${num.toLocaleString('vi-VN')} \u0111/m\u00b2`;
 }
 
+
+// ---------------------------------------------------------------------------
+// Alias: formatCompact
+// ---------------------------------------------------------------------------
+
+/**
+ * Alias for {@link formatPrice}.
+ * Use this name when the call-site intent is compact/abbreviated display
+ * rather than a full price string (e.g. chart tick labels, map markers).
+ */
+export const formatCompact = formatPrice;
+
 // ---------------------------------------------------------------------------
 // Parser (reverse direction)
 // ---------------------------------------------------------------------------