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 path. The main changes are:

• Guided rubber bindings, slots, autofit, and editor commands.
• Physical round-cord collider generation with Legacy fallback.
• Physical slingshot authoring, validation, packaging, and inspector tools.
• Package serialization for guided rubber state and physical rubber settings.

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 physical collider generation and falls back to Legacy collision when guided data is not usable.
VisualPinball.Unity/VisualPinball.Unity/VPT/Rubber/RubberColliderComponent.cs	Adds rubber collider mode, physical material storage, and guided-path availability checks.
VisualPinball.Unity/VisualPinball.Unity/VPT/Rubber/RubberComponent.cs	Adds guided rubber state, baked path storage, restore helpers, and detach/reset behavior.
VisualPinball.Unity/VisualPinball.Unity.Editor/VPT/Rubber/RubberInspector.cs	Adds guided-path editing UI with delayed binding changes and failed-bake rollback.
VisualPinball.Unity/VisualPinball.Unity.Editor/VPT/Rubber/RubberColliderInspector.cs	Adds collider model selection and prevents enabling Physical mode without a valid guided bake.

_{Reviews (3): 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.