Tomatoes, match tabs, shared pings, and a round of fixes

- On the results, everyone but the winner splats tomatoes where they
  click (bots aim at the winner), with a new splat sound.
- During a match the menu has the item tabs (choosing when the
  countdown allows, and otherwise levelling the sandbox's levels for
  when you're back), Play (the game's rules) and Settings.
- Pings are shared through the server (protocol 4), so other players'
  connection bars show over their heads and on their windows.
- PvP comes into lobbies with your profile and is saved.
- The choice menu opens by itself however the countdown began.
- Knocked-out fighters keep their buttons current, so Ready on the
  results toggles once per press.
- The weapon wheel wraps both ways. Readying with empty slots plays
  the equip sound for your own fighter.
- Shock Absorber: up to 50% less weapon movement and 33% less
  knockback. Only the catalog previews the next level.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/protocol.h

@@ -27,7 +27,7 @@
 #include <string_view>
 #include <type_traits>
 
-constexpr int PROTOCOL_VERSION = 3;
+constexpr int PROTOCOL_VERSION = 4;
 constexpr int LOBBY_MEMBERS_MAX = 16;
 constexpr int LOBBY_CODE_LENGTH = 4;
 // Letters only, without I and O, so codes are easy to read out and type.
@@ -49,6 +49,7 @@ constexpr int SERVER_URL_LENGTH = 128;
 //   PACKET_CHAT      Uint16 length, text
 //   PACKET_TYPING    Uint8 isTyping
 //   PACKET_RENAME    Uint16 length, text
+//   PACKET_PING      Uint16 milliseconds                        this player's round trip to the server
 //
 // Server to game:
 //   PACKET_STATE     room, tick, state                          the game this player is in now, as a tick starts
@@ -58,7 +59,7 @@ constexpr int SERVER_URL_LENGTH = 128;
 //                                                               once the events before them are in, and how early
 //                                                               (in ticks) this player's last controls came
 //   PACKET_CHECKSUM  room, tick, Uint32                         the room's state as that tick starts
-//   PACKET_CHAT      from, Uint16 length, text                  and the same for typing and renames
+//   PACKET_CHAT      from, Uint16 length, text                  and the same for typing, renames and pings
 enum PacketType : unsigned char
 {
     PACKET_PROFILE = 1,
@@ -70,7 +71,8 @@ enum PacketType : unsigned char
     PACKET_STATE,
     PACKET_EVENT,
     PACKET_FRAMES,
-    PACKET_CHECKSUM
+    PACKET_CHECKSUM,
+    PACKET_PING
 };
 
 // Packets are plain values one after another, as they sit in memory (every platform agrees on these layouts).