M152: Add support anchor spacing V1

[Coasterpete]

Summary

Implements Milestone 152: Support Anchor Spacing V1.

This milestone adds a backend-only support anchor spacing system to Quantum.Track that generates canonical station-distance support anchor candidates. It is intended as the first layer of a future procedural support pipeline and deliberately avoids renderer, terrain, or mesh dependencies.

Features

• Adds a SupportAnchorSpacingGenerator for deterministic anchor candidate generation.

• Supports:

  • Start distance
  • End distance
  • Target spacing
  • Optional start offset
  • Excluded distance ranges

• Produces:

  • Anchor candidate distances
  • Actual spacing intervals
  • Start/end remainder information
  • Non-fatal warnings for invalid inputs, excluded candidates/gaps, and uneven end remainders

• Includes focused unit tests covering:

  • Exact spacing
  • Offset spacing
  • End remainder behavior
  • Excluded ranges
  • Invalid inputs
  • Deterministic output

• Adds documentation for Support Anchor Spacing V1.

Non-Goals

This milestone intentionally does not:

• Snap anchors to terrain
• Generate support geometry
• Select support prefabs
• Create meshes
• Introduce Unity or renderer dependencies
• Modify TrackEvaluator

Those capabilities will be implemented in future milestones on top of this backend foundation.

Validation

dotnet test QuantumCoasterWorks.sln --nologo

Results

• Passed: 1729
• Failed: 0
• Skipped: 0

Future Work

Future milestones can build on this foundation by adding:

• Terrain snapping
• Support placement visualization
• Procedural support generation
• Support mesh generation
• Editor integration for live support previews