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/session.h

@@ -18,22 +18,6 @@ constexpr int SNAPSHOT_RING = 64;
 // A member's connection has no ping to show (it's this screen's own, hosting).
 constexpr float PING_NONE = -2;
 
-// 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] = {};
-};
-
 enum SessionEventType
 {
     EVENT_JOIN,