feat: add auto-repair at vendor open

When 'Auto Repair' is enabled in Settings > Gameplay, all damaged
equipment is automatically repaired when opening any armorer vendor
(canRepair=true). The repair is skipped when no items are actually
damaged to avoid a pointless server round-trip. A system chat message
confirms the repair. Setting persists to ~/.wowee/settings.cfg as
auto_repair.

include/ui/game_screen.hpp

@@ -196,6 +196,7 @@ private:
     bool pendingShowKeyring = true;
     bool pendingAutoLoot = false;
     bool pendingAutoSellGrey = false;
+    bool pendingAutoRepair = false;
 
     // Keybinding customization
     int pendingRebindAction = -1;  // -1 = not rebinding, otherwise action index