feat(web): AVM v2 upgraded valuation dashboard (TEC-2763)

R5.4 ships the upgraded AVM UI behind the `avm_v2` A/B flag. When the
flag is on, the dashboard exposes:

- Tab switch between single valuation and multi-property compare
- Waterfall drivers chart (ValueDriversChart) alongside the existing
  horizontal bar breakdown
- Mapbox comparables map with similarity-coloured markers and an
  optional highlighted subject pin
- Confidence interval + range bar and PDF export remain available
- Valuation history chart surface unchanged (still lazy-loaded)

Flag plumbing (useAvmV2Flag):
- NEXT_PUBLIC_FEATURE_AVM_V2=1 enables by default
- `?avm_v2=1|0` URL param forces + persists to localStorage
- safe localStorage handling (no throw when storage is blocked)

Tests: comparables-map, value-drivers-chart, use-avm-v2-flag specs
added. Pre-existing "Yếu tố chính" assertion in valuation-results.spec
updated to match the current copy ("Yếu tố ảnh hưởng giá") so the
valuation suite is green (7 files, 52 tests).

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/web/components/valuation/__tests__/valuation-results.spec.tsx

@@ -64,7 +64,7 @@ describe('ValuationResults', () => {
 
   it('renders price drivers section', () => {
     render(<ValuationResults result={mockResult} />);
-    expect(screen.getByText('Yếu tố chính')).toBeInTheDocument();
+    expect(screen.getByText('Yếu tố ảnh hưởng giá')).toBeInTheDocument();
     expect(screen.getByText(/Vị trí trung tâm/)).toBeInTheDocument();
     expect(screen.getByText(/Tầng thấp/)).toBeInTheDocument();
   });
@@ -82,7 +82,7 @@ describe('ValuationResults', () => {
   it('hides drivers section when empty', () => {
     const noDrivers = { ...mockResult, priceDrivers: [] };
     render(<ValuationResults result={noDrivers} />);
-    expect(screen.queryByText('Yếu tố chính')).not.toBeInTheDocument();
+    expect(screen.queryByText('Yếu tố ảnh hưởng giá')).not.toBeInTheDocument();
   });
 
 });