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/data/LeaderboardEntry.java

@@ -0,0 +1,45 @@
+package com.loki.lomines.data;
+
+import java.util.Objects;
+import java.util.UUID;
+
+/**
+ * Immutable data class representing a single entry in the leaderboard.
+ * Contains a player's UUID and their block count.
+ */
+public final class LeaderboardEntry {
+    
+    private final UUID playerId;
+    private final long count;
+    
+    public LeaderboardEntry(UUID playerId, long count) {
+        this.playerId = Objects.requireNonNull(playerId, "playerId cannot be null");
+        this.count = count;
+    }
+    
+    public UUID getPlayerId() {
+        return playerId;
+    }
+    
+    public long getCount() {
+        return count;
+    }
+    
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+        LeaderboardEntry that = (LeaderboardEntry) o;
+        return count == that.count && playerId.equals(that.playerId);
+    }
+    
+    @Override
+    public int hashCode() {
+        return Objects.hash(playerId, count);
+    }
+    
+    @Override
+    public String toString() {
+        return "LeaderboardEntry{playerId=" + playerId + ", count=" + count + "}";
+    }
+}