Preview Data Generator

Generates two tightly-coupled things for a SwiftUI view:

1. Sample data tuned for the Xcode canvas — realistic instances plus the visual edge cases that break layouts (empty, one item, huge list, long/overflowing strings, missing images, error and loading states).
2. A #Preview matrix — the variant blocks you'd otherwise hand-write to prototype and QA a view across light/dark, Dynamic Type, locale/RTL, device sizes, and data states.

This is the design-time counterpart to testing/test-data-factory (which makes fixtures for the test suite). Where a factory already exists, this skill reuses Model.fixture() instead of inventing parallel data.

When This Skill Activates

Use this skill when the user:

• Wants sample/mock data for Xcode previews ("what do I put in the preview?")
• Wants to preview a view in multiple states (empty / loading / error / loaded)
• Is prototyping UI and wants light/dark, Dynamic Type, RTL, or device variants
• Says "add previews", "preview matrix", "preview this in dark mode + large text"
• Has a SwiftData @Model and needs an in-memory seeded container for previews
• Is on Xcode 16 / iOS 18 and wants shared, cached preview data via PreviewModifier