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/data/modular-architecture/00-MODULAR-ARCHITECTURE-GUIDE.md

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+# Modular Component Architecture
+
+**Navigation hub for the three-tier specification system**
+
+---
+
+## Foundation (00-)
+
+### [Agent-Designer Collaboration](00-foundation/agent-designer-collaboration.md)
+
+How AI agents optimize designer craft without replacing designer thinking
+
+---
+
+## Core Concepts (01-)
+
+### [Three-Tier Architecture](01-core-concepts/three-tier-overview.md)
+
+Overview of Pages, Components, and Features separation
+
+### [Content Placement Rules](01-core-concepts/content-placement-rules.md)
+
+Decision tree for where to document content
+
+### [Complexity Detection](01-core-concepts/complexity-detection.md)
+
+How to identify simple vs complex components
+
+---
+
+## Workflows (02-)
+
+### [Page Specification Workflow](02-workflows/page-specification-workflow.md)
+
+Step-by-step page decomposition from sketch to specs
+
+### [Complexity Router Workflow](02-workflows/complexity-router-workflow.md)
+
+Guided decomposition for complex components
+
+### [Storyboard Integration](02-workflows/storyboards/storyboards-guide.md)
+
+Using visual storyboards for complex components
+
+---
+
+## Examples
+
+### [Simple Component Example](examples/simple-button.md)
+
+Button - single file documentation
+
+### [Complex Component Example](examples/complex-calendar.md)
+
+Calendar - three-tier decomposition
+
+### [Search Bar Example](examples/search-bar.md)
+
+Search with page-specific content
+
+---
+
+## Quick References (03-)
+
+### [Decision Tree](03-quick-refs/decision-tree.md)
+
+One-page flowchart for file placement
+
+### [Benefits Summary](03-quick-refs/benefits.md)
+
+Why this architecture works