Implement shape skirt adhesion type

[Copilot]

PR #104 added the adhesion framework with 'circular' and 'shape' skirt subtypes, but only circular was implemented. Shape skirt now follows the actual first layer outline instead of using a circular approximation.

Changes

Slicing pipeline

• Extract first layer paths during mesh slicing and pass to adhesion module
• Compute paths before adhesion generation to enable shape-following

Shape skirt implementation

• Custom polygon offset algorithm (createOutsetPath) expands paths outward using perpendicular normals
• Filters holes by point-in-polygon testing, processes only outer boundaries
• Generates concentric loops at adhesionDistance + (loopIndex × nozzleDiameter)
• Falls back to circular skirt when first layer paths unavailable

API consistency

• Updated brim and raft modules to accept firstLayerPaths parameter for future use
• Maintains uniform interface across all adhesion types

Usage

const slicer = new Polyslice({
  adhesionEnabled: true,
  adhesionType: 'skirt',
  adhesionSkirtType: 'shape',  // or 'circular'
  adhesionDistance: 5,
  adhesionLineCount: 3
});

const gcode = slicer.slice(mesh);

Shape skirt adapts to geometry (box → square, cylinder → circular, complex → follows outline), while circular skirt uses fixed radius regardless of shape.

Original prompt

Excellent work in PR 104 (#104) adding the necessary framework for an adhesion module. We successfully added a ‘skirt’ adhesion type with two subtypes ‘circular’ skirt and ‘shape’ skirt. However, only the circular skirt has been implemented. Could you now please attempt to implement the ‘shape’ skirt? Thanks!

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