Implement Dark Mode for Map (Leaflet) and Info Labels

Currently, dark mode is applied only to the search section.
Leaflet supports dark-themed maps.

Why:
Dark map theme improves eye comfort and consistency.

Issues noticed:
Map does not switch to dark mode
Info labels/popups remain in light mode after enabling dark theme via buttons

Expected:
Dark theme applied to map
Info labels/popups follow dark mode consistently
