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/note-inline-editor.tsx

@@ -565,7 +565,7 @@ export function NoteInlineEditor({
               {isProcessingAI
                 ? <Loader2 className="h-3.5 w-3.5 animate-spin" />
                 : <Sparkles className="h-3.5 w-3.5" />}
-              <span className="hidden sm:inline">IA Note</span>
+              <span className="hidden sm:inline">{t('ai.aiNoteTitle')}</span>
             </Button>
           )}