[UserList] Fix join/spectate from the profile hover card doing nothing (#7383)

The games list in the profile hover card offered "Join game" and
"Spectate", but UserInfoPopup::joinGameRequested was only forwarded to an
identical UserListWidget::joinGameRequested signal that nothing connected
to. Clicking either entry sent no command, opened no tab and showed no
error.

Route the request to TabSupervisor, which owns the join flow. The popup's
games list spans every room the user is in, so the target room may not be
open yet; IntentJoinServerGame already joins the room first and retries,
which is why this goes through the intent rather than straight to
GameSelector.

Extract the intent construction that joinReportGame already had into a
shared joinGameByIntent helper instead of duplicating it.

Also stop disabling "Join game" for games that are full or already
running. GameSelector::joinGame() offers to join as a spectator in that
case, so a greyed-out entry read as a dead button; GameSelector's own
context menu never disables it either.

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

cockatrice/src/interface/widgets/server/user/user_info_popup.cpp

@@ -634,9 +634,10 @@ void UserInfoPopup::onGamesContextMenu(const QPoint &pos)
                        "QMenu::item:selected{background:%4;}")
             .arg(colorStr(theme.bg), colorStr(theme.text), colorStr(theme.border), colorStr(theme.buttonHover)));
 
-    const bool canJoin = !game.started() && game.player_count() < game.max_players();
+    // Never grey the join action out: GameSelector::joinGame() asks whether to
+    // fall back to spectating when the game is full or already running, so a
+    // disabled entry would just read as a dead button.
     QAction *join = menu.addAction(tr("Join game"));
-    join->setEnabled(canJoin);
 
     QAction *spec = nullptr;
     if (game.spectators_allowed()) {