refactor: split MineConfig and Mines classes (291→182, 247→157 lines)

- Extract MineConfig.Builder → MineConfigBuilder (separate file)
- Split Mines into 3 services:
  * MineFileManager - file operations
  * MineRepository - CRUD operations
  * MaskScanService - mask scanning logic
- Fix imports: data.* → data.config.*

Progress: 2/7 files >200 lines fixed

src/main/java/com/loki/lomines/handler/MineRewardHandler.java

@@ -1,7 +1,7 @@
 package com.loki.lomines.handler;
 
 import com.loki.lomines.LoMinesPlugin;
-import com.loki.lomines.data.MineConfig;
+import com.loki.lomines.data.config.MineConfig;
 import com.loki.lomines.data.Reward;
 import org.bukkit.Material;
 import org.bukkit.block.Block;