test(maps): stub maplibre-gl-leaflet globally

jsdom has no WebGL, so the real vector basemap layer can never work in the
client tests. More immediately: several map tests hand react-leaflet a partial
useMap() stub with no addLayer on it, which was harmless while the basemap was
a stubbed <TileLayer> and is not now that it is a real layer - addTo() reaches
for map.addLayer and rejects into the void. 79 unhandled rejections, every
assertion still green, and vitest fails the run on those.

Stubbed in the setup file for the same reason ResizeObserver is: the capability
does not exist in this environment. The tests that assert on the layer register
their own mock, which takes precedence.

client/tests/setup.ts

@@ -100,3 +100,25 @@ if (typeof URL.createObjectURL === 'undefined') {
 
 // Element.prototype.scrollIntoView — jsdom doesn't implement it
 Element.prototype.scrollIntoView = vi.fn();
+
+// maplibre-gl-leaflet — the vector basemap every Leaflet map draws since the move
+// off CARTO. jsdom has no WebGL, so the real layer can never work here; more to
+// the point, several map tests hand react-leaflet a partial `useMap()` stub, and
+// the real layer's addTo() reaches for map.addLayer and rejects into the void.
+// Stubbed globally for the same reason ResizeObserver is: the capability does not
+// exist in this environment. Tests that assert on the layer register their own
+// mock, which takes precedence over this one.
+vi.mock('@maplibre/maplibre-gl-leaflet', () => ({
+  maplibreGL: vi.fn(() => {
+    const gl = {
+      setStyle: vi.fn(),
+      on: vi.fn(),
+      isStyleLoaded: vi.fn(() => false),
+      getStyle: vi.fn(() => ({ layers: [] })),
+      setLayoutProperty: vi.fn(),
+    };
+    const layer: Record<string, unknown> = { remove: vi.fn(), getMaplibreMap: vi.fn(() => gl) };
+    layer.addTo = vi.fn(() => layer);
+    return layer;
+  }),
+}));