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-4-ux-design/data/modular-architecture/03-quick-refs/decision-tree.md

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+# Content Placement Decision Tree
+
+**One-page flowchart for file placement**
+
+---
+
+## The Decision Tree
+
+```
+┌─────────────────────────────────────────────────┐
+│  Does CONTENT vary by page context?             │
+│  (text, images, data source)                    │
+└────────────┬────────────────────────────────────┘
+             │
+      ┌──────┴──────┐
+      │             │
+     YES            NO
+      │             │
+      ▼             ▼
+┌─────────────┐  ┌──────────────┐
+│ Page File   │  │ Feature File │
+│             │  │              │
+│ Document:   │  │ Document:    │
+│ - Headings  │  │ - Generic    │
+│ - Text      │  │   content    │
+│ - Images    │  │ - Default    │
+│ - Data API  │  │   config     │
+│ - Scope     │  │              │
+└─────────────┘  └──────────────┘
+```
+
+---
+
+## Examples
+
+**Page File (Content Varies):**
+
+- ✅ Hero heading: "Welcome" (Home) vs "About" (About)
+- ✅ Search placeholder: "Search products..." vs "Search help..."
+- ✅ Calendar header: "Familjen Svensson: Vecka 40" (user's family)
+- ✅ Data API: `/api/families/:currentFamilyId/walks` (user-specific)
+
+**Feature File (Content Same Everywhere):**
+
+- ✅ Button text: "Submit" (always the same)
+- ✅ Error message: "Invalid email" (generic validation)
+- ✅ Tooltip: "Click to expand" (generic interaction)
+- ✅ Data API: `/api/products` (same for all users)
+
+---
+
+## Visual Design?
+
+```
+Is this VISUAL design (colors, spacing, states)?
+│
+└─ YES → Component File
+         (Colors, typography, layout, states)
+```
+
+---
+
+## Quick Rule
+
+- **Page File** = WHERE + WHAT (page-specific)
+- **Component File** = HOW IT LOOKS (visual design)
+- **Feature File** = WHAT IT DOES (functionality + generic content)