Superadmin impersonation, hardened auth/upload paths, dependency updates

- Add superadmin impersonation: sessions.impersonated_by (migration 0003) is
  stamped onto audit rows so impersonated actions are attributable, with a
  persistent ImpersonationBanner in the app shell.
- Harden auth and upload handling across routes (safe redirect targets,
  filename sanitization, checkout grant handling).
- Update dependencies: Sentry 8 -> 10, @fastify/static 8 -> 10,
  react-router-dom 6.30.6; add find-my-way / fast-uri overrides.
- Add tests for safe-next, checkout-grant, and upload-filename.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/api/test/checkout-grant.test.ts

@@ -0,0 +1,66 @@
+import { describe, it, expect } from 'vitest';
+
+// Mirrors the grant decision in src/routes/webhooks-stripe.ts. `checkout.session.completed` fires
+// as soon as Checkout finishes, which for delayed-notification payment methods (ACH debit, bank
+// transfer, some wallets) happens BEFORE any money moves — payment_status 'unpaid'. Granting on
+// the event alone hands out a paid plan for an unsettled payment.
+type PaymentStatus = 'paid' | 'unpaid' | 'no_payment_required';
+
+function shouldGrantPlan(paymentStatus: PaymentStatus): boolean {
+  return paymentStatus === 'paid' || paymentStatus === 'no_payment_required';
+}
+
+// Mirrors the subscription-status branch in the same file.
+type SubStatus =
+  | 'active'
+  | 'trialing'
+  | 'past_due'
+  | 'unpaid'
+  | 'canceled'
+  | 'incomplete'
+  | 'incomplete_expired';
+
+function planForSubscription(status: SubStatus): 'pro' | 'starter' | null {
+  if (status === 'active' || status === 'trialing') return 'pro';
+  if (status === 'unpaid' || status === 'incomplete_expired') return 'starter';
+  return null; // leave the current plan untouched
+}
+
+describe('checkout grant decision', () => {
+  it('grants on a settled payment', () => {
+    expect(shouldGrantPlan('paid')).toBe(true);
+  });
+
+  it('grants when no payment was required (e.g. a 100% coupon)', () => {
+    expect(shouldGrantPlan('no_payment_required')).toBe(true);
+  });
+
+  it('withholds the plan while the payment is unsettled', () => {
+    // The regression this guards: a delayed-payment method completing Checkout unpaid used to
+    // grant 'lifetime' outright.
+    expect(shouldGrantPlan('unpaid')).toBe(false);
+  });
+});
+
+describe('subscription status mapping', () => {
+  it('treats only active and trialing as paying', () => {
+    expect(planForSubscription('active')).toBe('pro');
+    expect(planForSubscription('trialing')).toBe('pro');
+  });
+
+  it('does not upgrade on past_due, and does not downgrade mid-retry either', () => {
+    // Stripe is still retrying the charge — flipping the plan in either direction here would
+    // either hand out Pro for a failed renewal or cut off a customer whose retry succeeds.
+    expect(planForSubscription('past_due')).toBeNull();
+  });
+
+  it('drops to starter on terminal non-payment states', () => {
+    expect(planForSubscription('unpaid')).toBe('starter');
+    expect(planForSubscription('incomplete_expired')).toBe('starter');
+  });
+
+  it('leaves the plan alone for states that carry no payment signal', () => {
+    expect(planForSubscription('incomplete')).toBeNull();
+    expect(planForSubscription('canceled')).toBeNull(); // handled by subscription.deleted instead
+  });
+});