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/lib/__tests__/currency.spec.ts

@@ -2,6 +2,7 @@ import { describe, it, expect } from 'vitest';
 import {
   formatPrice,
   formatVND,
+  formatVNDFull,
   formatPricePerM2,
   parseVND,
 } from '../currency';
@@ -105,6 +106,31 @@ describe('formatPricePerM2', () => {
   });
 });
 
+// ---------------------------------------------------------------------------
+// formatVNDFull — full locale format, no compact notation
+// ---------------------------------------------------------------------------
+
+describe('formatVNDFull', () => {
+  it('formats with full locale number + đ suffix', () => {
+    expect(formatVNDFull(4_990_000)).toMatch(/4.*990.*000.*đ/);
+  });
+
+  it('never uses compact notation', () => {
+    const result = formatVNDFull(1_500_000_000);
+    expect(result).not.toContain('tỷ');
+    expect(result).toContain('đ');
+  });
+
+  it('handles zero and negatives', () => {
+    expect(formatVNDFull(0)).toMatch(/0.*đ/);
+    expect(formatVNDFull(-1)).toBe('0 đ');
+  });
+
+  it('accepts string input', () => {
+    expect(formatVNDFull('1500000')).toMatch(/1.*500.*000.*đ/);
+  });
+});
+
 // ---------------------------------------------------------------------------
 // parseVND — reverse parse
 // ---------------------------------------------------------------------------