Support uploading .geojson files directly

A .geojson file needs no GPX/FIT conversion — it's already the shape
gpx.js expects — so GpxStore#geojson now just reads and returns it
as-is, no cache sidecar. save/tree/the upload dropzone and its zip
handling all pick it up through the existing TRACK_EXTENSIONS list.

Also fixes a bug the new "cached" tree icon would have shipped with:
a GPX/FIT's own .geojson cache sidecar (e.g. "ride.gpx.geojson") also
matches the new .geojson branch in list_children, which would have
listed it as a second, phantom tree entry — excluded explicitly, with
a regression test.

lib/maptool/geojson.rb

@@ -0,0 +1,18 @@
+module Maptool
+  # A directly-uploaded .geojson file needs no conversion — GpxStore serves
+  # it straight from disk (see GpxStore#geojson) — so unlike Gpx/Fit there's
+  # no to_geojson here. Only kind-detection lives here, for the tree's badge
+  # icons, mirroring Gpx.kinds' cheap substring-search rather than a full
+  # JSON parse: a POI export can be tens of MB, geojson or not, and a full
+  # parse just to answer "does this have any points/lines" would cost the
+  # same either way.
+  module Geojson
+    def self.kinds(path)
+      content = File.read(path)
+      kinds = []
+      kinds << "waypoint" if content.include?('"Point"')
+      kinds << "track" if content.include?('"LineString"') # matches MultiLineString too
+      kinds
+    end
+  end
+end

lib/maptool/gpx_store.rb

@@ -2,6 +2,7 @@ require "fileutils"
 require "json"
 require_relative "gpx"
 require_relative "fit"
+require_relative "geojson"
 
 module Maptool
   # Filesystem-backed store for uploaded GPX/FIT files, organized in
@@ -110,9 +111,14 @@ module Maptool
     # can take tens of seconds, every single time the file is toggled
     # visible. Cached alongside the source file and invalidated by mtime,
     # so only the first read after a save (or edit) pays that cost.
+    #
+    # A directly-uploaded .geojson file skips all of this — it's already in
+    # the shape gpx.js expects, so there's nothing to convert or cache;
+    # it's just read and served as-is.
     def geojson(relative_path)
       path = resolve_file(relative_path)
       raise Errno::ENOENT, path unless File.file?(path)
+      return File.read(path) if path.downcase.end_with?(".geojson")
 
       cache = geojson_cache_path(path)
       unless geojson_cached?(path)
@@ -139,12 +145,16 @@ module Maptool
       "#{path}.geojson"
     end
 
+    # A .geojson source needs no separate cache file — it already is the
+    # target format, so it's always "ready".
     def geojson_cached?(path)
+      return true if path.downcase.end_with?(".geojson")
+
       cache = geojson_cache_path(path)
       File.file?(cache) && File.mtime(cache) >= File.mtime(path)
     end
 
-    TRACK_EXTENSIONS = %w[.gpx .fit].freeze
+    TRACK_EXTENSIONS = %w[.gpx .fit .geojson].freeze
 
     def safe_filename(filename)
       base = File.basename(filename.to_s)
@@ -176,6 +186,12 @@ module Maptool
           { "type" => "file", "name" => entry, "path" => rel, "kinds" => Gpx.kinds(full), "cached" => geojson_cached?(full) }
         elsif entry.downcase.end_with?(".fit")
           { "type" => "file", "name" => entry, "path" => rel, "kinds" => Fit.kinds(full), "cached" => geojson_cached?(full) }
+        # A GPX/FIT's own cache sidecar (e.g. "ride.gpx.geojson", written by
+        # `geojson` above) also ends in ".geojson" — excluded here so it
+        # doesn't show up as a second, phantom tree entry next to the file
+        # it was derived from.
+        elsif entry.downcase.end_with?(".geojson") && !entry.downcase.end_with?(".gpx.geojson", ".fit.geojson")
+          { "type" => "file", "name" => entry, "path" => rel, "kinds" => Geojson.kinds(full), "cached" => true }
         end
       end
     end