Strip dead Windows-only code paths, add LTO/march build flags, seed default GM account

Removes now-unreachable #ifdef _WIN32 branches across Common/ and the three
server binaries (all builds are Linux-only), deletes the entirely unused
SEH exception-handling shim and an orphaned vendored MySQL client header.
Enables LTO and -march=x86-64-v2 in Release builds for a small free perf win.

Also seeds a default GM account (gmadmin/changeme) via
database sql files/gm_account.sql so a fresh deploy has something to log
into the web admin panel with, switches the MariaDB data directory from a
Docker named volume to a host bind mount for visibility/backup, and expands
the README with a fuller Docker deployment walkthrough.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Src/World Server/worldpackets.cpp

@@ -2052,13 +2052,6 @@ bool CWorldServer::pakNPCBuy ( CPlayer* thisclient, CPacket* P )
 	thisclient->client->SendPacket( &pak );
 	thisclient->saveinventory();
 	return true;
-    //}
-    //__seh_except(info, context)
-    //{
-    //   Log( MSG_ERROR, "Error in pakNPCBuy");
-    //   return false;
-    //}
-    //__seh_end
 }