Add end-of-level tree QR share on results screen

[kenowagb]

Summary

• Track starting BST insertion order and numbers the player successfully places during a run (TreeRunTracker + TreeShareConfig).
• Generate a seemytree viewer QR at song end (TreeQrCodeGenerator / ZXing) and show it on the existing results screen beside performance stats.
• Works for 1P and 2P — each player gets their own tracker URL on their result panel.

Test plan

• Play GameScene (1P), place some nodes, finish the song
• Confirm results screen still shows grade/score/hits and Continue/Quit
• Confirm QR appears (no Scan text); Console logs viewer URL in editor/dev builds
• Scan QR → seemytree viewer URL matches starting sample order + successful placements only
• Finish with zero successful placements → URL still has placed= and QR still shows
• Failed Place attempts do not appear in placed
• 2P: each side’s QR reflects that player’s tree
• Change TreeShareConfig base URL in Inspector and confirm the encoded URL updates