feat: add encounter-level DPS/HPS tracking to DPS meter

Track cumulative player damage/healing for the full combat encounter
using the persistent CombatLog, shown alongside the existing 2.5s
rolling window. The encounter row appears after 3s of combat and
persists post-combat until the next engagement, giving a stable
full-fight average rather than the spiky per-window reading.

include/ui/game_screen.hpp

@@ -524,6 +524,9 @@ private:
     bool showDPSMeter_ = false;
     float dpsCombatAge_ = 0.0f;   // seconds in current combat (for accurate early-combat DPS)
     bool dpsWasInCombat_ = false;
+    float dpsEncounterDamage_ = 0.0f;  // total player damage this combat
+    float dpsEncounterHeal_   = 0.0f;  // total player healing this combat
+    size_t dpsLogSeenCount_   = 0;     // log entries already scanned
 
 public:
     void triggerDing(uint32_t newLevel);