ui: add side action bars, fix resize positioning, and fix player nameplates

Action bars:
- Expand from 2 bars (24 slots) to 4 bars (48 slots)
- Bar 2: right-edge vertical bar (slots 24-35), off by default
- Bar 3: left-edge vertical bar (slots 36-47), off by default
- New "Interface" settings tab with toggles and offset sliders for all bars
- XP bar Y position now tracks bar 2 visibility and vertical offset

HUD resize fix:
- All HUD elements (action bars, bag bar, XP bar, cast bar, mirror timers)
  now use ImGui::GetIO().DisplaySize instead of window->getWidth/Height()
- DisplaySize is always in sync with the current frame — eliminates the
  one-frame lag that caused bars to misalign after window resize

Player nameplates:
- Show player name only on nameplate (no level number clutter)
- Fall back to "Player (level)" while name query is pending
- NPC nameplates unchanged (still show "level Name")

include/ui/game_screen.hpp

@@ -115,6 +115,10 @@ private:
     bool pendingShowActionBar2 = true;   // Show second action bar above main bar
     float pendingActionBar2OffsetX = 0.0f;  // Horizontal offset from default center position
     float pendingActionBar2OffsetY = 0.0f;  // Vertical offset from default (above bar 1)
+    bool pendingShowRightBar = false;   // Right-edge vertical action bar (bar 3, slots 24-35)
+    bool pendingShowLeftBar  = false;   // Left-edge vertical action bar (bar 4, slots 36-47)
+    float pendingRightBarOffsetY = 0.0f;  // Vertical offset from screen center
+    float pendingLeftBarOffsetY  = 0.0f;  // Vertical offset from screen center
     int pendingGroundClutterDensity = 100;
     int pendingAntiAliasing = 0;  // 0=Off, 1=2x, 2=4x, 3=8x
     bool pendingNormalMapping = true;   // on by default