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/config.cpp

@@ -45,18 +45,6 @@ bool ConfigGetEntry( const char *pcFile, const char *pcNameMust, char* &pcResult
 		while ( *pcPar==' ' || *pcPar=='\t' || *pcPar=='=' ) ++pcPar;
 		*pcPoint=0;
 
-		#ifdef _WIN32
-		if ( !_strcmpi( pcName, pcNameMust ) )
-		{
-			pcResult = _strdup( pcPar );
-			pcPoint  = pcResult + strlen( pcPar );
-			if ( *pcPoint==0 ) return true;
-			--pcPoint;
-			while( *pcPoint==' ' || *pcPoint=='\t' ) *pcPoint--=0;
-			return true;
-		}
-
-		#else
 		if ( strcasecmp( pcName, pcNameMust )==0 )
 		{
 			pcResult = _strdup( pcPar );
@@ -66,7 +54,6 @@ bool ConfigGetEntry( const char *pcFile, const char *pcNameMust, char* &pcResult
 			while( *pcPoint==' ' || *pcPoint=='\t' ) *pcPoint--=0;
 			return true;
 		}
-		#endif
 
 	} while ( !feof( fh ) );