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/game/spell_defines.hpp

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <ctime>
 #include <string>
 #include <vector>
 
@@ -63,6 +64,19 @@ struct CombatTextEntry {
     bool isExpired() const { return age >= LIFETIME; }
 };
 
+/**
+ * Persistent combat log entry (stored in a rolling deque, survives beyond floating-text lifetime)
+ */
+struct CombatLogEntry {
+    CombatTextEntry::Type type = CombatTextEntry::MELEE_DAMAGE;
+    int32_t  amount       = 0;
+    uint32_t spellId      = 0;
+    bool     isPlayerSource = false;
+    time_t   timestamp    = 0;   // Wall-clock time (std::time(nullptr))
+    std::string sourceName;      // Resolved display name of attacker/caster
+    std::string targetName;      // Resolved display name of victim/target
+};
+
 /**
  * Spell cooldown entry received from server
  */