Character panel: minus buttons take back attribute and skill points

- respec: the panel's unused second button array becomes − buttons between
  name and value; attributes give back invested points, skills give back
  skill points, a level-1 skill is removed and can be chosen anew; all
  through the game's own point functions (protected copy stays in sync)
- the − is the + icon with its vertical arm covered (no minus image exists)
- hud: RenderCentred / HandleCentred for mods hooking centred windows;
  mouse event helpers shared in game/ui/events.h

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/mods/hud.h

@@ -17,4 +17,10 @@ void* CursorFor(void* cursor);
 // visible while no moved window was under the cursor) and are visible now.
 int VisibleDialogTooltips(void** out, int max);
 
+// For mods that hook a centred window themselves: run body(context) as the
+// HUD layer runs the window's render method (drawing shifted, the cursor seen
+// shifted) or event handler (mouse position shifted by the window's offset).
+int RenderCentred(void* window, int (*body)(void* context), void* context);
+int HandleCentred(void* event, int (*body)(void* context), void* context);
+
 } // namespace mods::hud