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/match.h

@@ -142,8 +142,25 @@ inline int pick_encode(bool isTrinket, int slot, int item)
         {.type = EDIT_ITEM, .isTrinket = isTrinket, .index = slot, .value = item < 0 ? EDIT_EMPTY : item});
 }
 
+// A player's setup as they join online: their name, the colour they'd like (-1 for any), and their sandbox slots,
+// loadouts, levels and stacking, which their fighter starts with. Plain data, sent as it sits in memory.
+struct Profile
+{
+    char name[PLAYER_NAME_MAX + 1] = {};
+    int color = -1;
+    int weaponSlots = SLOTS_DEFAULT;
+    int trinketSlots = SLOTS_DEFAULT;
+    int weaponLoadout[SLOT_MAX] = {};
+    int trinketLoadout[SLOT_MAX] = {};
+    int weaponSlotLevels[SLOT_MAX] = {};
+    int trinketSlotLevels[SLOT_MAX] = {};
+    int weaponItemLevels[WEAPON_COUNT] = {};
+    int trinketItemLevels[TRINKET_COUNT] = {};
+};
+
 // The default rules for a mode: a best-of-three deathmatch for two, or a three minute race for four.
 Rules rules_get(int mode);
+Profile profile_get(Fighter& fighter);
 Rules rules_clean(Rules rules);
 
 // Online, a game queued in the lobby's sandbox by one of its fighters: its rules, and the area on the ground where
@@ -221,6 +238,9 @@ public:
     int queue_startable_get(Sim& sim);
     bool is_queue_set(Sim& sim, int queuer);
     void queue_slots_shift(int from, int count);
+    int member_join(Sim& sim, int member, const Profile& profile);
+    void member_leave(Sim& sim, int member);
+    int fighter_find(Sim& sim, int member);
     int humans_left_get(Sim& sim);
 
 private: