Give Overpass POI downloads icons/descriptions and unique filenames

Overpass categories now carry the same icon+color styling a p4n2gpx
waypoint gets, instead of falling back to gpx.js's plain red marker,
plus a popup description built from opening_hours/operator/website
tags. Supermarket/convenience store reuse NPS's generic store glyph,
the only honest match in that icon set.

Each plugin run's saved filename now bakes in the area's center and a
timestamp, so repeated downloads for different areas land as separate,
identifiable files instead of overpass-pois.geojson/-1/-2/...

app.rb

@@ -356,13 +356,24 @@ module Maptool
       bbox = %w[south west north east].map { |key| params[key].to_s }
       halt 400, json(error: "south, west, north, east are required") if bbox.any?(&:empty?)
 
+      south, west, north, east = bbox.map(&:to_f)
       begin
-        geojson = Plugins.run(PLUGINS_DIR, params[:name], bbox.map(&:to_f))
+        geojson = Plugins.run(PLUGINS_DIR, params[:name], [south, west, north, east])
       rescue Plugins::RunError => e
         halt 502, json(error: e.message)
       end
 
-      path = GPX_STORE.save(folder: "", filename: "#{params[:name]}.geojson", io: StringIO.new(JSON.generate(geojson)))
+      # Filename carries the area's center and the run's timestamp (same
+      # idea as a p4n2gpx export's own "p4n_area_<lat>_<lon>_<date>_<time>"
+      # naming) — without it, running this again for a different area just
+      # overwrote/renamed-with-a-counter the same "overpass-pois.geojson",
+      # with nothing in the file tree to tell one run's POIs from another's.
+      center_lat = format("%.2f", (south + north) / 2)
+      center_lon = format("%.2f", (west + east) / 2)
+      timestamp = Time.now.strftime("%y%m%d_%H%M")
+      filename = "#{params[:name]}_#{center_lat}_#{center_lon}_#{timestamp}.geojson"
+
+      path = GPX_STORE.save(folder: "", filename: filename, io: StringIO.new(JSON.generate(geojson)))
       json path: path, tree: GPX_STORE.tree
     end