Add guide-driven physical rubber authoring

[freezy]

Summary

• import every VPX rubber as a modern manual Unity spline while keeping VPX collider and slingshot behavior in Legacy mode
• add stable guide support slots, circular post autofit, transactional guided rebakes, package round-trips, and editor authoring tools
• add a Physical round-cord collider model with swept-circle contacts and hardened slow/degenerate/transformed collision handling
• add calibrated physical slingshot authoring, validation, serialization, and device integration surfaces while keeping runtime actuation gated

Tests

• Unity 6000.5 EditMode: targeted rubber feature suite (47 passed)
• Unity 6000.5 EditMode: RubberSlingshotTests after final hardening (11 passed)
• Unity 6000.5 EditMode: RubberAutofitTests and SweptCircleColliderTests review-fix regression suite (33 passed)
• branch diff passes git diff --check

Compatibility

• VPX imports never autofit and always select the Legacy collider model
• VPX slingshot segments keep their existing legacy behavior
• experimental cord deformation and physical slingshot runtime registration remain unavailable pending calibration/runtime gates

[greptile-apps]

Greptile Summary

This PR adds guide-driven rubber authoring and a new physical rubber collision path. The main changes are:

• Guided rubber slots, autofit commands, inspectors, and dependency rebaking.
• Physical round-cord rubber collider generation with legacy fallback behavior.
• Rubber slingshot authoring, validation, packaging, and editor tooling.
• Package round-trip support for guided rubber and slingshot data.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
VisualPinball.Unity/VisualPinball.Unity/VPT/Rubber/RubberApi.cs	Adds legacy collision fallback when Physical rubber cannot use a current guided bake.
VisualPinball.Unity/VisualPinball.Unity.Editor/VPT/Rubber/RubberInspector.cs	Adds guided path editing with delayed, transactional binding updates.
VisualPinball.Unity/VisualPinball.Unity/VPT/Rubber/RubberComponent.cs	Stores guided rubber bindings, bake metadata, sampled paths, and reset helpers.
VisualPinball.Unity/VisualPinball.Unity/VPT/Rubber/RubberColliderComponent.cs	Adds Physical and Legacy collider mode state plus guided-path availability checks.

_{Reviews (2): Last reviewed commit: "rubber: harden invalid guided state" | Re-trigger Greptile}

[freezy]

Addressed both review findings in 31ba62d: guided binding edits now require a concrete slot and remain transactional, while invalid Physical rubber falls back to Legacy colliders. Focused autofit/collider tests pass 33/33.