Initial release: swift-front skill with Apple HIG integration

Combines frontend-design aesthetics with swiftui-pro correctness,
grounded in Apple's Human Interface Guidelines (134 articles).

Includes curated HIG reference files for typography, color, layout,
materials, motion, icons, and components, plus full HIG JSON data
for deep lookups.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

references/hig-materials.md

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+# HIG: Materials
+
+Source: [Apple HIG — Materials](https://developer.apple.com/design/human-interface-guidelines/materials)
+
+## Overview
+
+Two types of materials:
+1. **Liquid Glass** — Dynamic material for controls/navigation (tab bars, sidebars, toolbars)
+2. **Standard materials** — For visual differentiation within the content layer
+
+## Liquid Glass
+
+Forms a distinct functional layer floating above content. Content scrolls and peeks through.
+
+### Rules
+
+- **Don't** use Liquid Glass in the content layer — controls/navigation only
+- Exception: transient interactive elements (sliders, toggles) take Liquid Glass when activated
+- Use sparingly — system components get it automatically
+- Only apply to custom controls for the most important functional elements
+
+### Variants
+
+| Variant | Appearance | Use When |
+|---------|-----------|----------|
+| **Regular** | Blurs + adjusts luminosity | Background might affect legibility; significant text (alerts, sidebars, popovers) |
+| **Clear** | Highly translucent | Floating over media (photos, videos) for immersive experience |
+
+### Clear Variant Dimming
+
+- Bright underlying content: add dark dimming layer at 35% opacity
+- Dark underlying content or AVKit controls: no dimming needed
+
+### Color on Liquid Glass
+
+- No inherent color — takes on colors from content behind it
+- Apply color sparingly — reserve for primary actions (Done button accent)
+- Color the background, not symbols/text
+- Don't color multiple control backgrounds
+
+## Standard Materials
+
+### iOS/iPadOS
+
+Four levels (content layer only): ultra-thin, thin, regular (default), thick
+
+**Vibrancy for labels:** `label`, `secondaryLabel`, `tertiaryLabel`, `quaternaryLabel`
+**Vibrancy for fills:** `fill`, `secondaryFill`, `tertiaryFill`
+
+Avoid `quaternaryLabel` on thin/ultraThin (too low contrast).
+
+### macOS
+
+- Several standard materials with designated purposes
+- Two blending modes: **behind window** and **within window**
+
+### tvOS
+
+| Material | Recommended For |
+|----------|----------------|
+| ultraThin | Full-screen views, light scheme |
+| thin | Overlays, light scheme |
+| regular | General overlays |
+| thick | Overlays, dark scheme |
+
+### visionOS
+
+- Windows use system **glass** material (unmodifiable, adaptive)
+- No distinct Dark Mode — glass adapts to luminance behind it
+- Prefer translucency over opaque colors
+- Custom component materials: thin (interactive), regular (separations), thick (dark distinct)
+- Vibrancy: `label`, `secondaryLabel`, `tertiaryLabel`
+
+### watchOS
+
+- Use materials for context in full-screen modal views
+- Don't remove default material backgrounds from modal sheets
+
+## SwiftUI API
+
+- `.ultraThinMaterial`, `.thinMaterial`, `.regularMaterial`, `.thickMaterial`, `.ultraThickMaterial`
+- Liquid Glass: `glassEffect(_:in:)`