feat(scenegraph): add basic scene graph data structures

mini-nav/scenegraph/roomnode.py

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+from dataclasses import dataclass
+
+import numpy as np
+
+
+@dataclass
+class RoomNode:
+    room_id: str  # 例如: "room_A"
+
+    # 范围：不用复杂的 Polygon，用一个中心点+半径，或者简单的 3D BBox 足够了
+    center: np.ndarray  # [x, y, z]
+    bbox_extent: np.ndarray  # [dx, dy, dz] 用于快速判断一个点在不在房间里