chore: initial commit - LoMines v3.0.0 base structure

- Java rewrite from Kotlin
- LoAPI 3.0.0 integration
- Paper 1.21 support
- Core mine system with handlers
- BlockSetter abstraction (Bukkit/Oraxen/ItemsAdder)
- Statistics and leaderboard system
- Group wand for batch mine creation
- Mask fill mode support

Known issues:
- ConfigLoader.java: 712 lines (needs refactoring)
- MineCommands.java: 341 lines (needs splitting)
- 7 classes exceed 200 line limit
- Code quality improvements needed (KISS, DRY, SOLID)

src/main/java/com/loki/lomines/block/BlockSetter.java

@@ -0,0 +1,37 @@
+package com.loki.lomines.block;
+
+import com.loki.lomines.util.Cuboid;
+import org.bukkit.Location;
+
+import java.util.List;
+import java.util.function.IntConsumer;
+
+/**
+ * Abstract base class for block setting strategies.
+ * Provides a template for filling mine regions with blocks.
+ * 
+ * <p>Implementations:</p>
+ * <ul>
+ *   <li>BukkitBlockSetter - For vanilla Minecraft blocks</li>
+ *   <li>OraxenBlockSetter - For Oraxen custom blocks</li>
+ *   <li>ItemsAdderBlockSetter - For ItemsAdder custom blocks</li>
+ * </ul>
+ * 
+ * <p>This is a placeholder that will be fully implemented in task 2.7.</p>
+ */
+public abstract class BlockSetter {
+    
+    /**
+     * Fills a cuboid region with blocks asynchronously.
+     * The callback is invoked in the main thread after completion.
+     * 
+     * @param region The region to fill
+     * @param callback Called with the number of blocks set when complete
+     */
+    public abstract void fill(Cuboid region, IntConsumer callback);
+    
+    /**
+     * Places random weighted blocks only at the given locations (mask mode).
+     */
+    public abstract void fillAtLocations(List<Location> locations, IntConsumer callback);
+}