feat: implement hardcore hearts with game mode lock

Display hardcore heart textures when a world is in hardcore mode,
matching Java Edition behavior. Hearts switch between normal/hardcore
across all states (poison, wither, flash) and all HUD resolutions.

C++ changes:
- IUIScene_HUD: check isHardcore() and call SetHardcoreMode() each tick
- UIScene_HUD: send hardcore boolean to Flash via Iggy, invalidate
  SetHealth dirty check on state change to force heart redraw
- CreateWorldMenu/LoadMenu: lock game mode to Survival when hardcore
- MinecraftServer: gate server.properties hardcore override behind
  MINECRAFT_SERVER_BUILD so offline worlds preserve their saved flag

SWF changes (via new Java tools):
- AddHardcoreBitmaps: adds 10 hardcore heart bitmaps to graphics SWFs
- AddHardcoreHearts: adds 10 new frames (15-24) to health sprite
- PatchHudABC: patches HUD ActionScript bytecode with SetHardcore
  method and frame offset logic (+14 normal/poison, +6 wither)

Also updates README changelog styling with consistent ### headings.

Minecraft.Client/Common/UI/IUIScene_HUD.h

@@ -11,6 +11,7 @@ protected:
 	int m_iCurrentHealth;
 	int m_lastMaxHealth;
 	bool m_lastHealthBlink, m_lastHealthPoison, m_lastHealthWither;
+	bool m_lastHealthHardcore;
 	int m_iCurrentFood;
 	bool m_lastFoodPoison;
 	int m_lastAir, m_currentExtraAir;
@@ -46,6 +47,7 @@ protected:
 	virtual void SetActiveSlot(int slot) = 0;
 
 	virtual void SetHealth(int iHealth, int iLastHealth, bool bBlink, bool bPoison, bool bWither) = 0;
+	virtual void SetHardcoreMode(bool bHardcore) = 0;
 	virtual void SetFood(int iFood, int iLastFood, bool bPoison) = 0;
 	virtual void SetAir(int iAir, int extra) = 0;
 	virtual void SetArmour(int iArmour) = 0;