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/Common/log.cpp

@@ -1,8 +1,3 @@
-#ifdef _WIN32
-    #include <conio.h>
-    #include <windows.h>
-    #include <cstdio>
-#endif
 #include <cstdio>
 #include <cstdarg>
 #include <cstring>
@@ -38,12 +33,6 @@ static int __FOREGROUND = LIGHTGRAY;
 // Change console text color
 void textcolor(int color)
 {
-    #ifdef _WIN32
-    __FOREGROUND = color;
-	SetConsoleTextAttribute(GetStdHandle(STD_OUTPUT_HANDLE), color + (__BACKGROUND << 4));
-    #else
-
-    #endif
 }
 
 // This function logs based on flags