fix(map): import leaflet CSS statically so Vite emits the file

Dynamic await import of CSS only emits a JS shim (leaflet-src.HASH.js)
that injects styles at runtime, but the actual stylesheet file
(leaflet.HASH.css) is never written to dist/_astro/, causing 404s
on Astro's preload helper.

Static top-level import is processed at build time and emits the CSS.
Lazy-loading is preserved: the component still hydrates only with
client:media="(min-width: 900px)" in index.astro.

src/components/MapView.tsx

@@ -1,4 +1,5 @@
 import { useEffect, useRef } from 'preact/hooks';
+import 'leaflet/dist/leaflet.css';
 import type { Aviso } from '../lib/types';
 import { municipioCoords } from '../lib/fixtures';
 
@@ -18,7 +19,6 @@ export default function MapView({ avisos }: Props) {
 
     (async () => {
       const L = await import('leaflet');
-      await import('leaflet/dist/leaflet.css');
       if (!mapEl.current) return;
 
       map = L.map(mapEl.current, {