Park mods: name the Mods folder, not the server's path

- A missing mod folder reads "The mod folder "x" is not in the Mods folder."
  instead of printing where the server is installed; the reason can reach chat
  through an admin's command or a vote
- server_park_mods checks the exact message

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Y2G4APEkhHgVs59RDL3XWD

Server/Test/server_park_tests.cpp

@@ -195,7 +195,9 @@ int run(const std::filesystem::path &fixtures) {
             }
             return false;
         };
-        check(refused({"x", "not installed", "San Vansterdam", "bam"}, "is not in"), "A missing mod folder was not reported");
+        // Said without the server's own paths: the reason can reach chat (an admin, a vote).
+        check(refused({"x", "not installed", "San Vansterdam", "bam"}, "The mod folder \"not installed\" is not in the Mods folder."),
+              "A missing mod folder was not reported, or named the server's path");
         check(refused({"x", "popular skate 2 street park", "Isle of Grom", "grom"}, "has no park for grom"), "A missing park file was not reported");
         check(refused({"x", "two maps", "San Vansterdam", ""}, "set \"key\""), "A mod with parks for two maps did not ask for a key");
         check(load_park_mod(fixtures, {"x", "two maps", "Super Ultra Mega Resort", "mpr"}).objects.size() == 3, "A park chosen by its key did not load");

Server/server_parks.cpp

@@ -45,7 +45,7 @@ LoadedPark load_park_mod(const fs::path &mods, const ParkMod &park) {
     const auto folder = mods / fs::path(park.folder);
     std::error_code error;
     if (!fs::is_directory(folder, error))
-        throw std::runtime_error("The mod folder \"" + park.folder + "\" is not in " + path_utf8(mods) + ".");
+        throw std::runtime_error("The mod folder \"" + park.folder + "\" is not in the Mods folder.");
     const auto parks = folder / "parks";
     LoadedPark loaded;
     if (!park.key.empty() && !valid_park_key(park.key)) throw std::runtime_error("\"" + park.key + "\" is not a base map's key.");