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

memento-note/components/theme-initializer.tsx

@@ -7,9 +7,10 @@ interface ThemeInitializerProps {
   theme?: string
   fontSize?: string
   fontFamily?: string
+  accentColor?: string
 }
 
-export function ThemeInitializer({ theme, fontSize, fontFamily }: ThemeInitializerProps) {
+export function ThemeInitializer({ theme, fontSize, fontFamily, accentColor }: ThemeInitializerProps) {
   useEffect(() => {
     const applyFontSize = (s?: string) => {
       const size = s || 'medium'
@@ -54,7 +55,14 @@ export function ThemeInitializer({ theme, fontSize, fontFamily }: ThemeInitializ
     if (!localFontFamily && fontFamily) {
       localStorage.setItem('font-family', fontFamily)
     }
-  }, [theme, fontSize, fontFamily])
+
+    const localAccent = localStorage.getItem('accent-color')
+    const effectiveAccent = localAccent || accentColor || '#A47148'
+    document.documentElement.style.setProperty('--color-brand-accent', effectiveAccent)
+    if (!localAccent && accentColor) {
+      localStorage.setItem('accent-color', accentColor)
+    }
+  }, [theme, fontSize, fontFamily, accentColor])
 
   return null
 }