feat(billing): useStripeCheckout hook + post-redirect upgrade success

- useStripeCheckout: mutation + redirect full-page, pendingPriceType exposed
- PricingPage migré vers useStripeCheckout (suppression useMutation inline)
- useUpgradeSuccessHandler: détecte ?upgrade=success, invalide plan cache, clean URL
- UpgradeSuccessBanner: callout success dans DashboardPage
- Tests: 203 → 212 verts (+9)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/features/dashboard/hooks/__tests__/useUpgradeSuccessHandler.test.tsx

@@ -0,0 +1,88 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest'
+import { renderHook, act } from '@testing-library/react'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import type { ReactNode } from 'react'
+
+import { PLAN_QUERY_KEY } from '@/entities/user/query-keys'
+import { useUpgradeSuccessHandler } from '../useUpgradeSuccessHandler'
+
+let invalidateSpy: ReturnType<typeof vi.fn>
+let queryClient: QueryClient
+
+function wrapper({ children }: { children: ReactNode }) {
+  return <QueryClientProvider client={queryClient}>{children}</QueryClientProvider>
+}
+
+function setLocation(search: string) {
+  window.history.replaceState(null, '', `/dashboard${search}`)
+}
+
+beforeEach(() => {
+  queryClient = new QueryClient({
+    defaultOptions: { queries: { retry: false } },
+  })
+  invalidateSpy = vi.fn().mockResolvedValue(undefined)
+  // Spy sur la méthode invalidateQueries pour vérifier la clé exacte.
+  queryClient.invalidateQueries = invalidateSpy as unknown as typeof queryClient.invalidateQueries
+})
+
+afterEach(() => {
+  setLocation('')
+})
+
+describe('useUpgradeSuccessHandler', () => {
+  it('?upgrade=success → showSuccess=true, invalidate(PLAN_QUERY_KEY) appelé, URL nettoyée', () => {
+    setLocation('?upgrade=success')
+
+    const { result } = renderHook(() => useUpgradeSuccessHandler(), { wrapper })
+
+    expect(result.current.showSuccess).toBe(true)
+    expect(invalidateSpy).toHaveBeenCalledTimes(1)
+    expect(invalidateSpy).toHaveBeenCalledWith({ queryKey: PLAN_QUERY_KEY })
+    // URL nettoyée : plus de `upgrade` dans la query string.
+    expect(window.location.search).toBe('')
+  })
+
+  it('absence de query param → showSuccess=false, invalidate non appelé', () => {
+    setLocation('')
+
+    const { result } = renderHook(() => useUpgradeSuccessHandler(), { wrapper })
+
+    expect(result.current.showSuccess).toBe(false)
+    expect(invalidateSpy).not.toHaveBeenCalled()
+  })
+
+  it("?upgrade=cancelled (autre valeur) → showSuccess=false, pas d'action", () => {
+    setLocation('?upgrade=cancelled')
+
+    const { result } = renderHook(() => useUpgradeSuccessHandler(), { wrapper })
+
+    expect(result.current.showSuccess).toBe(false)
+    expect(invalidateSpy).not.toHaveBeenCalled()
+    // URL conservée intacte (autre valeur, hors scope du nettoyage).
+    expect(window.location.search).toBe('?upgrade=cancelled')
+  })
+
+  it('dismiss() bascule showSuccess à false', () => {
+    setLocation('?upgrade=success')
+
+    const { result } = renderHook(() => useUpgradeSuccessHandler(), { wrapper })
+    expect(result.current.showSuccess).toBe(true)
+
+    act(() => {
+      result.current.dismiss()
+    })
+    expect(result.current.showSuccess).toBe(false)
+  })
+
+  it('conserve les autres query params (utm_*, etc.) lors du nettoyage', () => {
+    setLocation('?upgrade=success&utm_source=email&ref=abc')
+
+    renderHook(() => useUpgradeSuccessHandler(), { wrapper })
+
+    const params = new URLSearchParams(window.location.search)
+    expect(params.has('upgrade')).toBe(false)
+    expect(params.get('utm_source')).toBe('email')
+    expect(params.get('ref')).toBe('abc')
+  })
+})