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/tests/unit/brainstorm-billing.test.ts

@@ -0,0 +1,140 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest'
+import {
+  billingOwnerFromSession,
+  getBillingOwner,
+} from '@/lib/brainstorm-collab'
+import {
+  checkSessionEntitlementOrThrow,
+  incrementUsageAsync,
+  QuotaExceededError,
+} from '@/lib/entitlements'
+
+const { prismaMock } = vi.hoisted(() => ({
+  prismaMock: {
+    subscription: { findUnique: vi.fn() },
+    brainstormSession: { findUnique: vi.fn() },
+  },
+}))
+
+vi.mock('@/lib/prisma', () => ({
+  prisma: prismaMock,
+  default: prismaMock,
+}))
+
+vi.mock('@/lib/redis', () => ({
+  redis: {
+    get: vi.fn(),
+    mget: vi.fn(),
+    eval: vi.fn(),
+  },
+}))
+
+vi.mock('@/lib/byok', () => ({
+  hasAnyActiveByok: vi.fn().mockResolvedValue(false),
+}))
+
+import { redis } from '@/lib/redis'
+import { hasAnyActiveByok } from '@/lib/byok'
+
+function mockActiveSubscription(tier: string) {
+  prismaMock.subscription.findUnique.mockResolvedValue({
+    userId: 'host-1',
+    tier: tier as any,
+    status: 'ACTIVE' as any,
+    currentPeriodStart: new Date(),
+    currentPeriodEnd: new Date(),
+  } as any)
+}
+
+describe('brainstorm host-pays billing (Story 3.4)', () => {
+  beforeEach(() => {
+    vi.clearAllMocks()
+  })
+
+  describe('billingOwnerFromSession', () => {
+    it('returns host id for host actor', () => {
+      expect(billingOwnerFromSession('host-1', 'host-1')).toEqual({
+        billingOwnerId: 'host-1',
+        isGuestActor: false,
+      })
+    })
+
+    it('returns host id for guest actor', () => {
+      expect(billingOwnerFromSession('host-1', 'guest-9')).toEqual({
+        billingOwnerId: 'host-1',
+        isGuestActor: true,
+      })
+    })
+  })
+
+  describe('getBillingOwner', () => {
+    it('loads session and resolves billing owner', async () => {
+      prismaMock.brainstormSession.findUnique.mockResolvedValue({ userId: 'host-1' })
+
+      const result = await getBillingOwner('session-abc', 'guest-9')
+      expect(result).toEqual({ billingOwnerId: 'host-1', isGuestActor: true })
+    })
+  })
+
+  describe('checkSessionEntitlementOrThrow', () => {
+    it('throws QuotaExceededError with guest metadata when host quota exhausted', async () => {
+      mockActiveSubscription('BASIC')
+      vi.mocked(redis.eval).mockResolvedValue(-1)
+
+      await expect(
+        checkSessionEntitlementOrThrow('host-1', 'guest-9', true, 'brainstorm_expand'),
+      ).rejects.toMatchObject({
+        billingOwnerId: 'host-1',
+        triggeredByUserId: 'guest-9',
+        isGuestActor: true,
+      })
+    })
+
+    it('increments host redis key when guest action bills host', async () => {
+      mockActiveSubscription('PRO')
+      vi.mocked(redis.eval).mockResolvedValue(1)
+
+      await checkSessionEntitlementOrThrow('host-1', 'guest-9', true, 'brainstorm_expand')
+
+      expect(redis.eval).toHaveBeenCalled()
+      const keyArg = String(vi.mocked(redis.eval).mock.calls[0]?.[2])
+      expect(keyArg).toContain('host-1')
+      expect(keyArg).not.toContain('guest-9')
+
+      const allKeyArgs = vi.mocked(redis.eval).mock.calls.map(call => String(call[2]))
+      const guestKeyUsed = allKeyArgs.some(k => k.includes('guest-9'))
+      expect(guestKeyUsed).toBe(false)
+    })
+  })
+
+  describe('host BYOK bypass (Story 3.5)', () => {
+    it('reserveUsage still runs when host has BYOK (bypass is per-provider in route layer)', async () => {
+      vi.mocked(hasAnyActiveByok).mockResolvedValue(true)
+      mockActiveSubscription('BASIC')
+      vi.mocked(redis.eval).mockResolvedValue(-1)
+
+      await expect(
+        checkSessionEntitlementOrThrow('host-1', 'guest-9', true, 'brainstorm_expand'),
+      ).rejects.toThrow()
+    })
+  })
+
+  describe('QuotaExceededError.toJSON', () => {
+    it('includes isGuestActor in toJSON for 402 responses', () => {
+      const err = new QuotaExceededError('PRO', 'brainstorm_expand', 10, 10, false, {
+        billingOwnerId: 'host-1',
+        triggeredByUserId: 'guest-9',
+        isGuestActor: true,
+      })
+      expect(err.toJSON()).toEqual({
+        error: 'QUOTA_EXCEEDED',
+        feature: 'brainstorm_expand',
+        upgradeTier: 'PRO',
+        byokConfigured: false,
+        isGuestActor: true,
+      })
+      expect(err.billingOwnerId).toBe('host-1')
+      expect(err.triggeredByUserId).toBe('guest-9')
+    })
+  })
+})