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/api/user/api-keys/[provider]/route.ts

@@ -0,0 +1,56 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { auth } from '@/auth';
+import { prisma } from '@/lib/prisma';
+import { VALID_PROVIDERS } from '@/lib/ai/router';
+
+type RouteContext = { params: Promise<{ provider: string }> };
+
+export async function PATCH(req: NextRequest, context: RouteContext) {
+  const session = await auth();
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  }
+
+  const { provider } = await context.params;
+  if (!VALID_PROVIDERS.has(provider)) {
+    return NextResponse.json({ error: 'Unknown provider' }, { status: 400 });
+  }
+
+  const body = (await req.json().catch(() => ({}))) as { isActive?: boolean };
+  if (typeof body.isActive !== 'boolean') {
+    return NextResponse.json({ error: 'isActive boolean required' }, { status: 400 });
+  }
+
+  const updated = await prisma.userAPIKey.updateMany({
+    where: { userId: session.user.id, provider },
+    data: { isActive: body.isActive },
+  });
+
+  if (updated.count === 0) {
+    return NextResponse.json({ error: 'Not found' }, { status: 404 });
+  }
+
+  return NextResponse.json({ ok: true });
+}
+
+export async function DELETE(_req: NextRequest, context: RouteContext) {
+  const session = await auth();
+  if (!session?.user?.id) {
+    return NextResponse.json({ error: 'Unauthorized' }, { status: 401 });
+  }
+
+  const { provider } = await context.params;
+  if (!VALID_PROVIDERS.has(provider)) {
+    return NextResponse.json({ error: 'Unknown provider' }, { status: 400 });
+  }
+
+  const deleted = await prisma.userAPIKey.deleteMany({
+    where: { userId: session.user.id, provider },
+  });
+
+  if (deleted.count === 0) {
+    return NextResponse.json({ error: 'Not found' }, { status: 404 });
+  }
+
+  return NextResponse.json({ ok: true });
+}