自写物理引擎的3D鲁布·戈德堡装置,自动运行

Build a 3D Rube Goldberg machine that runs itself, as a single self-contained index.html in the current directory.

The chain, in order:
1. A marble is released at the top and rolls down a series of zig-zag ramps.
2. It knocks over a line of at least 12 dominoes.
3. The last domino tips a seesaw, which launches a small ball into a hanging bucket.
4. The bucket's weight pulls it down; its rope runs over a pulley and yanks a bell, which visibly swings.
5. The same motion raises a flag up a pole. The flag reaching the top is the finish.

Rules:
- Write the physics yourself: no physics library. Every motion after the marble is released must come from your simulation (rigid bodies, collisions, constraints, rope/pulley). No keyframed animation or tweened motion of any machine part.
- You may load three.js from a CDN for rendering. Nothing else external: no images, models, or fonts.
- It must run with no user input: start automatically on page load, use a cinematic camera that follows the action, and complete the whole chain in about 15–20 seconds. After the flag is up, hold for 2 seconds, then reset and replay.
- Deterministic: fixed timestep and no unseeded randomness, so every run looks the same.
- Fill the browser window. It will be screen-recorded at 1280×720.
- No on-screen text or UI of any kind.
- Make it look good: lighting, shadows, materials, and a setting that makes it feel like a real contraption.