refactor: remove SaveTeachingPoint from IRobot

[DanielKow]

Summary

Removes int SaveTeachingPoint(string name, Pose3<double> pose) from IRobot (added in SDK 1.21.0). It is over-engineering and is removed before anything depends on it.

Why

• Persistence is not a device concern. Storing named teaching points belongs to the application layer (EventStore), not the vendor-agnostic robot interface.
• It cannot be honored on the real hardware. The Fairino controller exposes no SDK write path for teaching points, so a faithful implementation is impossible — only the simulator could implement it, which makes the contract misleading.
• Nothing consumes it. rocket-welder2 is pinned to SDK 1.16.0; the only implementation was SimulatedRobot (which simply delegated to its own SetTeachingPoint and returned 0).

Changes

• Delete the SaveTeachingPoint declaration + XML doc from RocketWelder.SDK.Automation/IRobot.cs.
• Remove the implementation from RocketWelder.SDK.Robotics.Core/SimulatedRobot.cs. The simulator-only SetTeachingPoint method (used directly by tests) is unaffected.

Verification

• dotnet build RocketWelder.SDK.sln — 0 errors.
• RocketWelder.SDK.Robotics.Core.Tests — 236 passed, 0 failed.