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

.agents/skills/wds-6-asset-generation/data/styles/content-styles/illustration.md

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+# Illustration
+
+## Overview
+Hand-crafted digital illustrations — custom, warm, and brand-unique.
+
+## Rendering Characteristics
+
+| Property | Value |
+|----------|-------|
+| **Detail level** | Medium — stylized, not photographic |
+| **Lighting** | Flat or gently shaded |
+| **Texture** | Smooth with subtle grain |
+| **Color** | Brand palette, can be limited |
+| **Depth** | Flat to moderate depth |
+
+## Prompt Keywords
+`illustration, digital illustration, hand-drawn, custom art, vector style, flat illustration, character illustration`
+
+## Best For
+- Brand storytelling, onboarding flows, empty states, error pages
+- Distinctive brand identity that photography can't deliver
+
+## Dimensions Guide
+- Spot illustrations: 400x400 to 800x800
+- Scene illustrations: 16:9 or custom
+- Icons as illustrations: 64x64 to 256x256