Closes #57.

Summary

This normalizes freehand pressure for non-pen pointer input while preserving real pressure for pen input.

Today BaseModel.getMousePosition() forwards raw event.pressure for every pointer type. StylusModel then feeds those points into perfect-freehand with:

• thinning: 0.9
• simulatePressure: false

That means non-pen inputs (mouse, touch) can produce different saved freehand geometry at the same nominal brush size, depending on the platform/browser's reported pressure behavior.

Change

Use real pressure only for pens:

pressure: event.pointerType === 'pen' ? event.pressure : 0.5

This is applied in both coordinate paths of BaseModel.getMousePosition().

Why 0.5

0.5 is the conventional active-pressure baseline for hardware without meaningful pressure support, and it matches the desktop mouse baseline that many browsers already use.

Scope

• preserves Apple Pencil / pen pressure behavior
• normalizes mouse and touch to the same freehand pressure baseline
• does not change line/rect/ellipse behavior beyond using the same point pressure normalization when applicable

Verification

• pnpm install --frozen-lockfile
• pnpm build
• locally verified downstream that the resulting freehand SVG geometry for synthetic mouse vs touch input at the same brush size becomes consistent after this patch