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-4-ux-design/templates/instructions/meta-content.instructions.md

@@ -0,0 +1,37 @@
+# Meta Content & Social Sharing
+
+**Include when:** Page is Public (SEO/social sharing needed)
+
+---
+
+## Page Title
+**Limit:** 55-60 characters
+
+`{title}`
+
+---
+
+## Meta Description
+**Limit:** 150-160 characters
+
+`{description}`
+
+---
+
+## Social Sharing
+
+| Property | Value |
+|----------|-------|
+| Title | {60-70 chars, can differ from page title} |
+| Description | {120-150 chars} |
+| Image | 1200x630px, `/images/social/{page-name}.jpg` |
+| Image Alt | {alt text} |
+
+---
+
+## Agent Questions
+
+1. "What should appear in browser tab/search results?" (< 60 chars)
+2. "Describe this page to encourage clicks" (150-160 chars)
+3. "What title for social shares?"
+4. "What image represents this page?" (1200x630px)