Route every Mercure publish through an event, log pushes per-player

Every $hub->publish() call site (chat, hints, security alerts, virus
alerts, game_finished, and the pre-game lobby events) now dispatches
a PushMercureMessageEvent instead of publishing directly. Two
listeners handle it: PublishMercureMessageListener does the actual
Mercure publish exactly as before (same wire format, no client
changes needed), and LogMercureMessageListener appends it to the
activity log of whichever player(s) it was actually delivered to.

A private /chat to one agent only gets logged for that agent, never
broadcast into everyone's transcript - the event carries an explicit
targetScreen (null = everyone) rather than leaving listeners to guess
from the payload shape.

The per-player log format moved from flat text to JSON Lines (one
timestamped, structured entry per line) via a new shared
SessionActivityLogger service, since a flat string can't carry an
event's type or exact payload - both needed for a future feature to
replay a player's full session history, not just their own commands,
on page reload. The admin session log viewer now parses and
formats these entries back into readable lines.

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

templates/game/admin/sessions/view.html.twig

@@ -98,7 +98,8 @@
                 font-size: 0.85rem;
                 line-height: 1.5;
                 margin: 0;
-            ">{{ playerLog.logs ?: 'No logs found for this player.' }}</pre>
+            ">{% if playerLog.entries is empty %}No logs found for this player.{% else %}{% for entry in playerLog.entries %}{% if entry.time %}[{{ entry.time }}] {% endif %}{{ entry.line }}
+{% endfor %}{% endif %}</pre>
         </div>
     {% endfor %}
 {% endblock %}