Add a search box, matching NPS's Park Tiles viewer

Top-left map control (topmost, above Home/zoom) with a text input:
"lat, lng" is parsed and jumped to directly (same plain-text shape the
topbar's coordinate readout already copies to the clipboard), anything
else is geocoded via Nominatim — OSM's own geocoder, free, no API key,
matching the online basemap's own OSM-derived style. Online only, same
story as this app's other non-basemap online features (Radar, the
Wikipedia layer) — no offline geocoding index to fall back to.

public/js/icons.js

@@ -62,6 +62,12 @@ export const SUNSET_ICON = `
   <path d="M9 10l3 3 3-3"/>
 </svg>`;
 
+export const SEARCH_ICON = `
+<svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round">
+  <circle cx="11" cy="11" r="7"/>
+  <path d="M20 20l-4.35-4.35"/>
+</svg>`;
+
 export const NEW_FOLDER_ICON = `
 <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.6" stroke-linecap="round" stroke-linejoin="round">
   <path d="M3 7a2 2 0 0 1 2-2h4l2 2h8a2 2 0 0 1 2 2v8a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V7z"/>