Dedicated server: park mods as server-owned objects

- maps.park_mods binds a Park Editor park mod (Mods/<folder>/parks/<key>.park.json)
  to a name and the map it was built on; maps.park_limits caps the parks and
  objects spawned at once (3 and 512 by default)
- park-mod list | add <name> [<name>...] [minutes] | remove <name> [<name>...] | clear,
  from the console, as /park-mod by admins, and by players through custom votes
- A spawned park is the layout of the server's own SteamID and epoch, sent like a
  player's: games since 1.0.0 already show it, it counts against no player's
  object limit, nobody can move or delete it, and it stays when players leave
- Objects players' games would not take (not Build Kit items, broken values) are
  skipped and logged; a missing or broken park is an error line when spawning
- Optional expiry (1-1440 min) with a warning in chat a minute before; every
  park goes on a map change and none survive a restart
- [parks] log lines name who did it: console, the admin, or "a vote"; a vote's
  refusal reaches chat
- park-mod is reserved for custom commands; README.txt documents the settings,
  commands and a park/unpark vote

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

Server/server_commands.cpp

@@ -27,6 +27,7 @@ constexpr std::string_view help_text =
     "announce <text> | announce-to <player> <text> | announcements [list|add <text>|remove <n>|clear|interval <minutes>|off]\n"
     "map-pool [add|remove <map>|clear] | rotation [<minutes>|off]\n"
     "park <lot> <layout> | park random | layer-sync on|off | layer <key> default|on|off | tod <time|default>\n"
+    "park-mod list | park-mod add <name> [<name>...] [minutes] | park-mod remove <name> [<name>...] | park-mod clear\n"
     "activity-log on|off | announce-throwdowns on|off | parties [on|off] | party-size <2-8> | afk-kick <minutes>|off | speed-check off|warn|kick | board-check off|warn|kick\n"
     "score-check [off|warn|kick] | score-allow [<fingerprint>|remove <fingerprint>]\n"
     "reserved [slots <n> | add|remove <SteamID64>] | roles [reload] | role <player or SteamID64> <role>|none | update | quit";
@@ -669,6 +670,7 @@ std::string Host::command(std::string_view line, std::uint64_t admin) {
         ++object_clears_;
         return changed("Deleted " + std::to_string(removed) + " placed object" + (removed == 1 ? "." : "s."));
     }
+    if (name == "park-mod") return park_mod_command(argument, admin);
     if (name == "park") {
         if (lower(argument) == "random") {
             config_.parks = random_park_choices();