`so101 setup` finds both arms, asks you to wiggle the leader, reuses existing calibration, then starts teleop #572

Piece 3 of 3 from #564, taken from closed pull #566 (src/setup.ts, src/arm-calibration.ts and their tests on refs/pull/566/head).

Done:

• [ ] bun so101 setup lists the USB adapters. With fewer than two it says "I see 1 arm. Plug in the other one, or check its power. Watching…" and goes on when a second appears.
• [ ] "Wiggle the arm you'll hold (the leader)" names both arms and saves the roles by USB serial number. whoIsTheLeader closes the first port when opening the second fails, with a test where spyOn(FeetechBus, "open") throws for the second path and the first FakeBus is closed. The test fails without the fix.
• [ ] Calibration reuses the servo's own ranges and LeRobot's ~/.cache/huggingface/lerobot/calibration/{robots,teleoperators}/*.json. It recalibrates only a joint that is out of range, one joint at a time, with a live bar.
• [ ] setup --dry-run prints the plan without touching a servo, and cli-node.test.ts runs it under Node.
• [ ] Setup ends in the teleop screen from the teleop piece. There is no share-on-web option.