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/brainstorm/invite-dialog.tsx

@@ -153,8 +153,8 @@ export function InviteDialog({
                   onClick={() => setRole('viewer')}
                   className={`flex-1 py-2.5 rounded-xl text-[10px] font-bold uppercase tracking-[0.1em] border transition-all ${
                     role === 'viewer'
-                      ? 'border-memento-blue/40 bg-memento-blue/5 text-memento-blue'
-                      : 'border-border text-muted-foreground hover:border-memento-blue/20'
+                      ? 'border-brand-accent/40 bg-brand-accent/5 text-brand-accent'
+                      : 'border-border text-muted-foreground hover:border-brand-accent/20'
                   }`}
                 >
                   {t('brainstorm.roleViewer') || 'Viewer'}