Geographical Map Widget

### What problem are you trying to solve?

DAC has no choropleth / geographic-map widget, and there's no escape hatch to add one in user code.

- JSX loader (`pkg/dashboard/jsloader.go:654`) passes unknown tags through, but `BruinWidgetFrame.tsx` only renders `metric / chart / table / text / divider / image` — unknown types render blank.
- TSX dashboards aren't a normal Vite/React build, so `react-leaflet` / `maplibre-gl` / `deck.gl` can't be imported.
- `` is `` only; `` strips raw HTML.

Today we either ship non-interactive PNG choropleths via ``, build a parallel Streamlit dashboard, or fork DAC.

### Proposed solution

First-class `` widget:

```tsx

```

Hover tooltip, zoom/pan, `` can drive `valueColumn`.

### Alternatives considered

- 2D `chart: heatmap` on binned lat/lon — pixel grid, not a map.
- Pre-rendered PNGs in `` — no interactivity.
- Streamlit alongside DAC — splits the dashboard layer.
- Fork DAC with a custom `MapWidget` — works, but per-user install + upstream drift.

### Additional context

Geographic views are high-leverage for any regional dataset (EU NUTS, US counties, country comparisons). Current PFAS investigation has 1,165 NUTS3 with metrics where the regional pattern is the story — bar charts hide it.