Stabilize Node 24 map tests by removing Leaflet DOM snapshot coupling

[Copilot]

The ci / unit-tests (24.x) failure came from a brittle MapModal snapshot that depended on Leaflet tile DOM/state, which varies across browser/runtime environments. This change makes the affected map tests deterministic by asserting stable rendered content instead of Leaflet internals.

• Replace flaky snapshot coverage

  • Remove the full-dialog snapshot from MapModal.test.tsx
  • Assert the visible map region and rendered marker content directly

• Mock react-leaflet in map tests

  • Replace runtime Leaflet DOM with a small test double for MapContainer, Marker, Popup, and TileLayer
  • Avoid environment-specific tile classes/styles such as leaflet-tile-loaded and transient opacity values

• Strengthen behavior-focused assertions

  • Verify marker content for the expected cities/counts
  • Add explicit coverage for singular formatting (1 visit from ...)
  • Keep OpenMapModalBtn filtering assertions focused on rendered marker count via stable test hooks

vi.mock('react-leaflet', () => ({
  MapContainer: ({ children }) => <div role="region" aria-label="Map">{children}</div>,
  Marker: ({ children }) => <div data-testid="marker">{children}</div>,
  Popup: ({ children }) => <>{children}</>,
  TileLayer: () => null,
}));

expect(screen.getAllByTestId('marker')).toHaveLength(expectedMarkers);
expect(screen.getByTestId('marker')).toHaveTextContent('1 visit from London');