feat: add persistent combat log window (/combatlog or /cl)

Stores up to 500 combat events in a rolling deque alongside the existing
floating combat text. Events are populated via the existing addCombatText()
call site, resolving attacker/target names from the entity manager and
player name cache at event time.

- CombatLogEntry struct in spell_defines.hpp (type, amount, spellId,
  isPlayerSource, timestamp, sourceName, targetName)
- getCombatLog() / clearCombatLog() accessors on GameHandler
- renderCombatLog() in GameScreen: scrollable two-column table (Time +
  Event), color-coded by event category, with Damage/Healing/Misc filter
  checkboxes, auto-scroll toggle, and Clear button
- /combatlog (/cl) chat command toggles the window

include/ui/game_screen.hpp

@@ -400,6 +400,10 @@ private:
     bool  showWhoWindow_ = false;
     void  renderWhoWindow(game::GameHandler& gameHandler);
 
+    // Combat Log window
+    bool  showCombatLog_ = false;
+    void  renderCombatLog(game::GameHandler& gameHandler);
+
     // Instance Lockouts window
     bool  showInstanceLockouts_ = false;