feat: design system overhaul — sidebar, AI chats, settings, brainstorm, color cleanup

- Sidebar: dynamic brand-accent colors, brainstorm section restyled
- AI chat general: popup panel with expand/collapse, hides when contextual AI open
- AI chat contextual: tabs reordered (Actions first), X close button, height fix
- Settings: all tabs restyled, 6 new color presets (sage, terracotta, iron, etc.)
- Global color cleanup: emerald/orange hardcoded → brand-accent dynamic
- Brainstorm page: orange → brand-accent throughout
- PageEntry animation component added to key pages
- Floating AI button: bg-brand-accent instead of hardcoded black
- i18n: all 15 locales updated with new AI/billing keys
- Billing: freemium quota tracking, BYOK, stripe subscription scaffolding
- Admin: integrated into new design
- AGENTS.md + CLAUDE.md project rules added

.agent/skills/wds-6-asset-generation/data/styles/design-styles/playful.md

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+# Playful
+
+## Overview
+Fun, energetic design with bold colors, rounded shapes, and a sense of joy.
+
+## Visual Characteristics
+
+| Property | Value |
+|----------|-------|
+| **Whitespace** | Moderate — lively but not cramped |
+| **Color palette** | Vibrant, multi-color, saturated |
+| **Typography** | Rounded, bold, sometimes quirky display fonts |
+| **Borders** | Rounded corners, chunky outlines |
+| **Shadows** | Colorful or offset shadows |
+| **Imagery** | Illustrations, cartoons, bright photography |
+| **Icons** | Filled, colorful, sometimes animated |
+
+## Prompt Keywords
+`playful, fun, colorful, energetic, vibrant, cheerful, friendly, whimsical, bouncy`
+
+## Best For
+- Children's products, games, education, creative tools, food delivery
+- Brands targeting younger audiences or wanting to feel approachable
+
+## Avoid
+- Luxury, finance, healthcare, legal services