/admin 'Try this P' runs the tuning experiment on the arm while nobody drives and keeps every result in the precision history #486

Replaces the rest of #451. When the owner presses the button on production, the real experiment runs, with no builder needed at the arm.

Done:

• [ ] POST /tuning/p {joint, p} on the arm server runs runPExperiment (#t). Its sweep is bench/limits-sweep.ts's fixed targets (#478), and its writes go through #450's guarded servo-params path. It is owner-only through the relay and same-origin. While a run is under way, a second one is a 409.
• [ ] Each result is appended to the precision history under the data directory, tagged with the deployed commit, and listed newest first in the admin Precision panel as joint, P from→to, before→after and kept or put back.
• [ ] The admin Servos section gets a 'Try this P' field and button per joint. It shows the run's progress and its result, or the refusal as a sentence.
• [ ] Tests against the fake bus: a run end to end that keeps, a run that puts the value back, a non-owner getting 404, and a run refused while someone drives.
• [ ] Safety limits, zones and the gripper torque cap are unchanged. bun --cwd Software/so101 test passes.

Parked by the crew: the preview's deploy failed and the decider saw no point in another try (pull #497 closed). Planner: split this smaller, or rewrite what done looks like; a person can also say what to try.