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/scenario-init/02-feature-selection.md

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+# Question 1: What Feature Delivers the Most Value?
+
+**Connect Trigger Map to the first thing you should design**
+
+---
+
+## The Question
+
+```
+Agent: "Looking at your Trigger Map and prioritized feature list,
+        what's the core feature that delivers value to your
+        primary target group?
+
+        This is what we should sketch first."
+```
+
+---
+
+## Why This Matters
+
+Your Trigger Map already identified:
+
+- Primary target group
+- What triggers their need
+- What outcome they want
+
+**This question connects that to a specific feature to design.**
+
+---
+
+## Example: Dog Week
+
+**From Trigger Map:**
+
+- Target: Parents
+- Trigger: Family conflict over dog care
+- Outcome: Accountability without nagging
+
+**Feature Selection:**
+
+```
+Designer: "The family dog walk calendar - it solves the accountability
+           problem that causes conflict."
+```
+
+**Why this feature first:**
+
+- Directly addresses the trigger (conflict)
+- Serves the primary target group (parents)
+- Delivers the desired outcome (accountability)
+
+---
+
+## What Agent Captures
+
+```
+CORE FEATURE: Family dog walk calendar
+WHY: Solves accountability problem that causes family conflict
+TARGET: Parents (primary decision makers)
+```
+
+---
+
+## Next Question
+
+[Where does the user first encounter this?](02-entry-point.md)
+
+---
+
+[← Back to Guide](00-SCENARIO-INIT-GUIDE.md)