Share online membership and game setup with the server

Profile, member join/leave and building a fresh game move into the sim library,
and the packet reader and writer into protocol.h, so the server can run lobbies
exactly as clients do.

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

src/sim.cpp

@@ -26,6 +26,53 @@ void Sim::tick()
     world.update(*this);
 }
 
+// A fresh online game for some of a lobby's fighters (by index) to play by the rules, bots filling the rest when the
+// rules say to. Their members, names and colours come along, and it starts from the seed, so everyone builds the same
+// one. The bots keep their difficulty.
+void Sim::game_start(Match& lobby, const int* members, int count, const Rules& rules, Uint32 seed)
+{
+    int owners[MAX_FIGHTERS];
+    int colors[MAX_FIGHTERS];
+    char names[MAX_FIGHTERS][PLAYER_NAME_MAX + 1];
+    for (int k = 0; k < count; k++)
+    {
+        owners[k] = lobby.owners[members[k]];
+        colors[k] = lobby.colors[members[k]];
+        std::memcpy(names[k], lobby.names[members[k]], sizeof(names[k]));
+    }
+    int players = rules.isBotFill ? std::max(rules.players, count) : count;
+    int level = bot.level;
+    bot = Bot{};
+    bot.level = level;
+    weapons = Weapons{};
+    world = World{};
+    match = Match{};
+    match.rules = rules;
+    match.rules.players = players;
+    match.isOnline = true;
+    rng.state = seed ? seed : RNG_SEED;
+    fighterCount = players;
+
+    bool isTaken[COLOR_COUNT] = {};
+    for (int k = 0; k < count; k++)
+        isTaken[colors[k] % COLOR_COUNT] = true;
+    for (int k = 0; k < players; k++)
+    {
+        fighters[k] = Fighter{};
+        fighters[k].init(*this, k);
+        match.owners[k] = k < count ? owners[k] : -1;
+        if (k < count)
+        {
+            match.colors[k] = colors[k];
+            std::memcpy(match.names[k], names[k], sizeof(match.names[k]));
+            continue;
+        }
+        match.colors[k] = std::find(isTaken, isTaken + COLOR_COUNT, false) - isTaken;
+        isTaken[match.colors[k]] = true;
+    }
+    match.start(*this);
+}
+
 // Moves a level by a step within the levels there are, cueing whether it went up or down.
 void level_step(Sim& sim, int& level, int step)
 {