feat: update EnvFlag materials for fire spread and burn flags for improved clarity

Author: ColdeZhang

src/main/java/cn/lunadeer/dominion/api/dtos/flag/Flags.java

@@ -41,11 +41,11 @@ public class Flags {
 
     // natural
     public static final EnvFlag FIRE_SPREAD
-            = new EnvFlag("fire_spread", "Fire Spread", "Prevent fire spread in dominion.", false, true, Material.CAMPFIRE);
+            = new EnvFlag("fire_spread", "Fire Spread", "Prevent fire spread in dominion.", false, true, Material.FLINT_AND_STEEL);
     public static final EnvFlag BURN_BLOCK
-            = new EnvFlag("burn_block", "Burn Block", "Whether blocks can burn.", false, true, Material.FIRE);
+            = new EnvFlag("burn_block", "Burn Block", "Whether blocks can burn.", false, true, Material.FIRE_CHARGE);
     public static final EnvFlag BURN_ENTITY
-            = new EnvFlag("burn_entity", "Burn Entity", "Whether entity can burn or take high-temperature damage (not including player).", false, true, Material.FIRE_CHARGE);
+            = new EnvFlag("burn_entity", "Burn Entity", "Whether entity can burn or take high-temperature damage (not including player).", false, true, Material.CAMPFIRE);
     public static final EnvFlag FLOW_IN_PROTECTION
             = new EnvFlag("flow_in_protection", "Flow In", "Prevent external water/lava flow into dominion.", false, true, Material.WATER_BUCKET);
     public static final EnvFlag GRAVITY_BLOCK