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/app/actions/semantic-search.ts

@@ -1,6 +1,8 @@
 'use server'
 
 import { semanticSearchService, SearchResult } from '@/lib/ai/services/semantic-search.service'
+import { auth } from '@/auth'
+import { checkEntitlementOrThrow, QuotaExceededError, incrementUsageAsync } from '@/lib/entitlements'
 
 export interface SemanticSearchResponse {
   results: SearchResult[]
@@ -20,6 +22,17 @@ export async function semanticSearch(
     notebookId?: string // NEW: Filter by notebook for contextual search (IA5)
   }
 ): Promise<SemanticSearchResponse> {
+  const session = await auth();
+  if (session?.user?.id) {
+    try {
+      await checkEntitlementOrThrow(session.user.id, 'semantic_search');
+    } catch (err) {
+      if (err instanceof QuotaExceededError) throw err;
+      console.error('[semantic-search] Quota check error (fail-open):', err);
+    }
+    incrementUsageAsync(session.user.id, 'semantic_search');
+  }
+
   try {
     const results = await semanticSearchService.search(query, {
       limit: options?.limit || 20,