feat: Implement Node class for D* Lite pathfinding algorithm with traversal cost calculation

server/pathfinding/Node.js

@@ -0,0 +1,61 @@
+/**
+ * Node - Represents a pathfinding node in the D* Lite algorithm
+ * Each node wraps a Point and stores pathfinding metadata
+ */
+import { Point } from './Point.js';
+
+export class Node {
+  constructor(point) {
+    this.point = point;
+    this.key = point.toKey();
+
+    // D* Lite values
+    this.g = Infinity;   // Cost from start to this node
+    this.rhs = Infinity; // One-step lookahead cost
+    
+    // Whether this node is blocked (wall, unbreakable block, etc.)
+    this.blocked = false;
+    
+    // Whether this node contains a mineable block (costs more to traverse but possible)
+    this.mineable = false;
+    
+    // The block data at this position (if known)
+    this.blockData = null;
+  }
+
+  /**
+   * Calculate the D* Lite key pair for priority queue ordering
+   * @param {Point} start - The current start position
+   * @param {number} km - The key modifier (updated on robot movement)
+   */
+  calculateKey(start, km = 0) {
+    const minVal = Math.min(this.g, this.rhs);
+    return [
+      minVal + start.euclideanDistanceTo(this.point) + km,
+      minVal
+    ];
+  }
+
+  /**
+   * Check if this node is consistent (g === rhs)
+   */
+  isConsistent() {
+    return this.g === this.rhs;
+  }
+
+  /**
+   * Get the traversal cost to move to this node
+   * - Blocked nodes: Infinity
+   * - Mineable blocks: 2 (higher cost to prefer open paths)
+   * - Open space: 1
+   */
+  getTraversalCost() {
+    if (this.blocked) return Infinity;
+    if (this.mineable) return 2;
+    return 1;
+  }
+
+  toString() {
+    return `Node(${this.point}, g=${this.g}, rhs=${this.rhs}, blocked=${this.blocked})`;
+  }
+}