Send a User-Agent to Overpass, overpass-api.de 406s Ruby's default

The Camper POIs plugin died with "plugin exited with status 1": Net::HTTP's
bare "Ruby" User-Agent now gets a 406 Not Acceptable from overpass-api.de,
any identifying one goes through.

lib/maptool/overpass_pois.rb

@@ -54,7 +54,11 @@ module Maptool
     def self.fetch(bbox, timeout: 60)
       query = build_query(bbox, timeout: timeout)
       uri = URI(OVERPASS_API)
-      response = Net::HTTP.post_form(uri, "data" => query)
+      # overpass-api.de answers Net::HTTP's default "Ruby" User-Agent with
+      # a 406 (verified 2026-10-09) — any identifying UA gets through.
+      request = Net::HTTP::Post.new(uri, "User-Agent" => "maptool (Overpass camper POIs plugin)")
+      request.set_form_data("data" => query)
+      response = Net::HTTP.start(uri.host, uri.port, use_ssl: true) { |http| http.request(request) }
       raise FetchError, "unexpected response #{response.code}" unless response.is_a?(Net::HTTPSuccess)
 
       JSON.parse(response.body)