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>