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/minimal.md

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+# Minimal
+
+## Overview
+Clean, spacious design with maximum whitespace and restrained use of elements.
+
+## Visual Characteristics
+
+| Property | Value |
+|----------|-------|
+| **Whitespace** | Generous — elements breathe |
+| **Color palette** | Monochrome + one accent |
+| **Typography** | Sans-serif, thin to regular weight |
+| **Borders** | Hairline or none |
+| **Shadows** | None or very subtle |
+| **Imagery** | High-contrast, isolated subjects |
+| **Icons** | Line icons, consistent stroke width |
+
+## Prompt Keywords
+`minimal, clean, whitespace, simple, uncluttered, modern, restrained, elegant simplicity`
+
+## Best For
+- Portfolio sites, luxury brands, SaaS products, personal sites
+- Content-focused layouts where text is primary
+
+## Avoid
+- Dense data displays, e-commerce with many products, playful brands