Fix three bugs found reviewing this session's changes

- notes.js's ICON_LABELS wasn't extended for the shop_supermarket/
  shop_convenience keys icons.js added — the note icon picker showed
  the raw internal key as the title instead of a real label.
- Plugins.run mislabeled a malformed plugin.json as "plugin did not
  print valid JSON" — a message written for bad script stdout, not a
  bad manifest, since both paths shared one rescue.
- overpass_pois.rb's description_for joined raw OSM tag values with
  "\n" — an operator/opening_hours tag with an embedded newline could
  inject an extra line into the popup that gpx.js's formatDescription
  (built for p4n2gpx's own well-formed lines) would render as its own
  independent, legitimate-looking link. Tag values are stripped of
  embedded newlines before joining.

lib/maptool/overpass_pois.rb

@@ -106,11 +106,22 @@ module Maptool
     private_class_method :category_for
 
     def self.description_for(tags)
-      lines = DESCRIPTION_TAGS.filter_map { |tag, label| "#{label}: #{tags[tag]}" if tags[tag] }
+      lines = DESCRIPTION_TAGS.filter_map { |tag, label| "#{label}: #{clean_tag(tags[tag])}" if tags[tag] }
       website = tags["website"] || tags["contact:website"]
-      lines << website if website
+      lines << clean_tag(website) if website
       lines.empty? ? nil : lines.join("\n")
     end
     private_class_method :description_for
+
+    # An OSM tag value is free text from a world-editable map — an embedded
+    # newline could otherwise inject an extra "line" of its own into the
+    # description, e.g. an operator tag ending in "\nhttps://evil.example"
+    # would render as its own separate, legitimate-looking link line once
+    # gpx.js's formatDescription (written for p4n2gpx's own well-formed
+    # "Label: value" lines) splits on "\n".
+    def self.clean_tag(value)
+      value.to_s.tr("\n\r", " ").strip
+    end
+    private_class_method :clean_tag
   end
 end

lib/maptool/plugins.rb

@@ -55,7 +55,11 @@ module Maptool
 
       manifest_path = File.join(plugin_dir, "plugin.json")
 
-      command = JSON.parse(File.read(manifest_path))["command"]
+      command = begin
+        JSON.parse(File.read(manifest_path))["command"]
+      rescue JSON::ParserError
+        raise RunError, "plugin has an invalid plugin.json"
+      end
       raise RunError, "plugin has no command" unless command
 
       south, west, north, east = bbox