Add physical drop target mechanics

[freezy]

Fixes #536.

Summary

• add opt-in Legacy, RothCompatible, and Mechanical drop-target physics modes while preserving Legacy as the default for existing content
• add explicit collider roles and package schema migration for front sensors, physical faces, and back faces
• reproduce the common Roth mass correction, brick classification, backside behavior, timing, and optional deterministic vertical bouncer without table scripts
• simulate Mechanical targets with finite effective mass, frictional contact, rear spring and stop, latch release/relatch, downward travel, down-stop rebound, reset motion, and moving-collider ball lift
• resolve simultaneous contacts in stable order and preserve the original collision ordering on tables without Mechanical targets
• support sliding and hinged target deflection, including point-dependent effective mass for hinged blades
• add reusable physics profiles, validation warnings, travel gizmos, runtime diagnostics, profiler markers, documentation, and VPX export warnings

Validation

• Unity 6.5 EditMode: 37/37 drop-target tests pass
• generated Unity solution compiles with zero errors
• DocFX builds with zero errors; the remaining FlipperApi xref warning is pre-existing and unrelated
• full branch diff passes git diff --check

Rollout notes

• the bundled Generic Sliding Blade profile is explicitly provisional and is not presented as measured real-machine calibration
• promoting a profile to measured still requires recorded mechanism data, held-out validation shots, and the documented 20-target performance benchmark
• VPX export retains ordinary target data but cannot preserve the advanced VPE physics settings

[greptile-apps]

Greptile Summary

This PR adds opt-in advanced drop-target physics. The main changes are:

• Legacy, Roth-compatible, and Mechanical physics modes.
• New collider roles and package fields for front, collision, and back meshes.
• Finite-mass mechanical target state, impact, reset, and switch behavior.
• Editor validation, runtime diagnostics, profiles, tests, and documentation.

Confidence Score: 4/5

The mechanical reset collision path needs a fix before merging.

• Passive back-face contacts can receive powered reset impulses.
• The issue is contained to mechanical drop-target reset and settle collisions.
• The package migration and legacy default paths look consistent from the inspected changes.

VisualPinball.Unity/VisualPinball.Unity/VPT/HitTarget/TargetCollider.cs

Important Files Changed

Filename	Overview
VisualPinball.Unity/VisualPinball.Unity/Game/PhysicsCycle.cs	Adds special grouping and reduction for mechanical drop-target contacts.
VisualPinball.Unity/VisualPinball.Unity/VPT/HitTarget/TargetCollider.cs	Adds mode-specific drop-target collision handling, with a role-filtering bug during reset contacts.
VisualPinball.Unity/VisualPinball.Unity/VPT/HitTarget/MechanicalDropTargetPhysics.cs	Adds the mechanical target state machine, impact solver, reset motion, and pose publishing.
VisualPinball.Unity/VisualPinball.Unity/VPT/HitTarget/DropTargetPackable.cs	Extends package data for physics modes, profiles, Roth settings, mechanical settings, and the third collider mesh.
VisualPinball.Unity/VisualPinball.Unity/VPT/HitTarget/DropTargetApi.cs	Adds mode-aware drop/reset commands and collider generation for the new target modes.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
  A[Ball hits mechanical drop target] --> B{Target resetting or settling?}
  B -->|Yes| C{Collider role is physical face?}
  C -->|Yes| D[Apply powered reset contact]
  C -->|No| E[Use passive wall or back-face collision]
  B -->|No| F{Collider role is physical face?}
  F -->|Yes| G[Apply mechanical face impact]
  F -->|No| E

Loading

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flowchart TD
  A[Ball hits mechanical drop target] --> B{Target resetting or settling?}
  B -->|Yes| C{Collider role is physical face?}
  C -->|Yes| D[Apply powered reset contact]
  C -->|No| E[Use passive wall or back-face collision]
  B -->|No| F{Collider role is physical face?}
  F -->|Yes| G[Apply mechanical face impact]
  F -->|No| E

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_{Reviews (1): Last reviewed commit: "physics: clean up drop target whitespace" | Re-trigger Greptile}