Randomize decoy usernames and which rapports carry coded messages

Decoy names in /var/home and verifyCodes.txt were a hardcoded 4-name
list (Luke, Charles, William, Peter), so a real player registering
under one of those names would collide with it. Now each session
picks 6 decoys from a pool of 10, excluding any name already taken by
a real player, and stores the pick as a session setting.

Likewise the 3 "special report" rapports that get coded messages were
always Doyle, Vega and Lennox. Each session now randomly assigns 3 of
the 20 rapports to that role, and the win screen / mainframe-help
message reference whichever agents were actually picked instead of
the hardcoded names.

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

templates/game/won.html.twig

@@ -62,7 +62,7 @@
                             Then the screens flood green: containment confirmed. The AI virus's grip on the server unravels file by file.
                         </p>
                         <p>
-                            Agents Doyle, Vega and Lennox are safe. Their identities were never decoded. In the days that follow,
+                            Agents {{ agentsText|default('Doyle, Vega and Lennox') }} are safe. Their identities were never decoded. In the days that follow,
                             the agency quietly credits an anonymous team of specialists for the save - you.
                         </p>
                     </div>