Add Mastermind and Hangman single-player games

- Mastermind: 4-color sequence, 10 tries, black/white peg feedback
- Hangman: 6 lives, progressive letter reveal, 10-word vocabulary
- Both available in BBS (telnet) and web (WML/XHTML) sides
- Shared sp_games persistence, scores table integration
- Updated games index and menu navigation

public_html/games.php

@@ -7,6 +7,8 @@ p_para('Single player:');
 p_links([
     ['/games/guess.php', 'Guess the Number'],
     ['/games/quiz.php',  'Quick Quiz'],
+    ['/games/mastermind.php', 'Mastermind'],
+    ['/games/hangman.php', 'Hangman'],
 ]);
 p_para('Multiplayer (play a friend):');
 p_links([