refactor(config): complete rewrite of configuration system

BREAKING CHANGE: New section-based configuration format

New Features:
- Type-safe BlockKey sealed interface (Vanilla, Oraxen, ItemsAdder)
- Section-based config: RegionConfig, BlockConfig, ResetConfig, RewardConfig, UIConfig, TeleportConfig
- Human-readable durations: 5m, 30s, 2h, 1d
- YAML inheritance from defaults.yml
- MiniMessage support for action bar and item names
- Immutable config records with validation

Removed:
- Legacy MineConfig (17-field god object)
- ConfigParser, ConfigValidator, ConfigSerializer split classes
- Legacy FillMode enum (replaced with better version)
- Old ConfigLoader with complex parsing logic

New Files:
- data/config/block/BlockKey.java - sealed interface for block types
- data/config/block/BlockConfig.java - type-safe block weights
- data/config/block/FillMode.java - fill strategies
- data/config/region/RegionConfig.java - region management
- data/config/reset/ResetConfig.java - reset behavior with Duration
- data/config/reward/RewardConfig.java - rewards with ItemReward
- data/config/teleport/TeleportConfig.java - teleport on reset
- data/config/ui/UIConfig.java - action bar and messages
- data/config/MineConfig.java - composed from sections
- data/config/ConfigLoader.java - clean loader with defaults inheritance
- defaults.yml - default configuration template

Tests:
- BlockKeyTest.java - serialization/deserialization
- BlockConfigTest.java - weight normalization, validation
- ResetConfigTest.java - duration parsing, defaults
- UIConfigTest.java - timer formatting, action bar
- MineConfigTest.java - builder, defaults, validation

src/main/java/dev/loki/lomines/data/config/region/RegionConfig.java

@@ -0,0 +1,99 @@
+package dev.loki.lomines.data.config.region;
+
+import dev.loki.lomines.util.location.Cuboid;
+import org.bukkit.Location;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * Configuration for mine regions.
+ * Immutable, validates regions on construction.
+ */
+public record RegionConfig(List<Cuboid> regions) {
+
+    public RegionConfig {
+        if (regions == null || regions.isEmpty()) {
+            throw new IllegalArgumentException("Mine must have at least one region");
+        }
+
+        // Defensive copy and validate
+        List<Cuboid> copy = List.copyOf(regions);
+
+        // Check all regions are in same world
+        String worldName = copy.get(0).getWorld().getName();
+        for (Cuboid region : copy) {
+            if (!region.getWorld().getName().equals(worldName)) {
+                throw new IllegalArgumentException(
+                        "All regions must be in the same world. Expected: " + worldName
+                );
+            }
+        }
+
+        regions = Collections.unmodifiableList(copy);
+    }
+
+    /**
+     * Creates a single-region config.
+     */
+    public static RegionConfig single(Cuboid region) {
+        return new RegionConfig(List.of(region));
+    }
+
+    /**
+     * Creates from paired locations (selection.1 + selection.2 = region 1).
+     * Selections must be even number.
+     */
+    public static RegionConfig fromSelections(List<Location> selections) {
+        if (selections.size() % 2 != 0) {
+            throw new IllegalArgumentException(
+                    "Selections must be in pairs (even number). Got: " + selections.size()
+            );
+        }
+
+        var regions = new java.util.ArrayList<Cuboid>();
+        for (int i = 0; i < selections.size(); i += 2) {
+            Location loc1 = selections.get(i);
+            Location loc2 = selections.get(i + 1);
+
+            if (!Objects.equals(loc1.getWorld(), loc2.getWorld())) {
+                throw new IllegalArgumentException(
+                        "Selection pair " + (i / 2 + 1) + " has locations in different worlds"
+                );
+            }
+
+            regions.add(new Cuboid(loc1, loc2));
+        }
+
+        return new RegionConfig(regions);
+    }
+
+    /**
+     * Total volume of all regions.
+     */
+    public int totalVolume() {
+        return regions.stream().mapToInt(Cuboid::getVolume).sum();
+    }
+
+    /**
+     * World name (all regions share the same world).
+     */
+    public String worldName() {
+        return regions.get(0).getWorld().getName();
+    }
+
+    /**
+     * Checks if location is within any region.
+     */
+    public boolean contains(Location location) {
+        return regions.stream().anyMatch(r -> r.contains(location));
+    }
+
+    /**
+     * Number of regions.
+     */
+    public int regionCount() {
+        return regions.size();
+    }
+}