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-1-project-brief/templates/project-brief-dialog/04-concept.md

@@ -0,0 +1,82 @@
+# Step 4: Product Concept
+
+**Completed:** {{date}}
+**Session:** {{session_number}}
+
+---
+
+## Purpose
+
+Capture the designer's STRUCTURAL vision - the founding principle or key feature that defines the product concept.
+
+**Not just requirements - the IDEA.**
+
+---
+
+## Concept Exploration
+
+**Agent asked:**
+{{question_to_surface_concept}}
+
+**User described:**
+{{concept_description}}
+
+---
+
+## Deep Dive
+
+### Core Structural Idea
+
+**The founding principle:**
+{{what_makes_this_product_distinct}}
+
+**Concrete example:**
+{{specific_example_of_concept_in_action}}
+
+### Why This Matters
+
+**User's rationale:**
+{{why_this_approach}}
+
+**Problem it solves:**
+{{what_this_enables}}
+
+---
+
+## Reflection Checkpoint
+
+**Agent's synthesis:**
+{{understanding_of_concept}}
+
+**User response:**
+- [ ] Confirmed
+- [ ] Corrected
+
+**Corrections (if any):**
+{{corrections}}
+
+---
+
+## Concept Documentation
+
+**Core concept:**
+{{concept_statement}}
+
+**Implementation principle:**
+{{how_this_shapes_design}}
+
+**Example:** {{concrete_example}}
+
+---
+
+## Related Features
+
+Features that stem from this concept:
+1. {{feature_1}}
+2. {{feature_2}}
+3. {{feature_3}}
+
+---
+
+**Documented in:** `wds-project-outline.yaml` → `product_concept`
+**Impacts:** Navigation structure, information architecture, feature priorities