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/notes-editorial-view.tsx

@@ -328,7 +328,7 @@ function NoteTag({ labelName, allLabels }: { labelName: string; allLabels: any[]
   
   return (
     <div className="inline-flex items-center gap-1.5 px-2 py-0.5 rounded-md bg-paper dark:bg-white/5 text-[9px] font-bold uppercase tracking-[0.15em] text-muted-foreground border border-border/40">
-      {isAI && <Sparkles size={8} className="text-blueprint" />}
+      {isAI && <Sparkles size={8} className="text-brand-accent" />}
       {labelName}
     </div>
   )