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.

views/layout.erb

@@ -43,6 +43,7 @@
         "/js/panels.js": "/js/panels.js?v=<%= ASSET_VERSION %>",
         "/js/plugins.js": "/js/plugins.js?v=<%= ASSET_VERSION %>",
         "/js/radar.js": "/js/radar.js?v=<%= ASSET_VERSION %>",
+        "/js/search.js": "/js/search.js?v=<%= ASSET_VERSION %>",
         "/js/shadow.js": "/js/shadow.js?v=<%= ASSET_VERSION %>",
         "/js/sun.js": "/js/sun.js?v=<%= ASSET_VERSION %>",
         "/js/track_profile.js": "/js/track_profile.js?v=<%= ASSET_VERSION %>"