feat: add temporary hazardous barriers in hard mode

include/game_render.h

@@ -32,6 +32,8 @@ struct RenderAssets {
     u16 *gfx_tail_v[2] = {nullptr, nullptr};
     u16 *gfx_apple_rotten = nullptr;
     u16 *gfx_apple_cursed = nullptr;
+    u16 *gfx_barrier = nullptr;      // Solid, fatal barrier segment
+    u16 *gfx_barrier_warn = nullptr; // Dashed outline shown while announcing
 
     HudCache hudCache;
 };
@@ -41,5 +43,7 @@ void draw_game(const GameState &state, const RenderAssets &assets);
 void draw_stats(const GameState &state, RenderAssets &assets, bool internals, bool musicEnabled, uint8_t frame);
 void draw_menu(const GameState &state, RenderAssets &assets, bool musicEnabled);
 void blink_apples(const GameState &state, u16 *gfx_apple);
+// Called every VBlank: owns OAM slots [0, BARRIER_OAM_SLOTS) and animates barrier palette entries
+void draw_barriers(const GameState &state, const RenderAssets &assets, uint8_t frame);
 
 #endif