docs: add comprehensive Stripe billing guide

Covers architecture, configuration steps, user flows, API routes,
webhooks, pricing, testing with Stripe CLI, production checklist,
and troubleshooting.

memento-note/hooks/use-cookie-consent.ts

@@ -0,0 +1,40 @@
+'use client'
+
+import { useCallback, useEffect, useState } from 'react'
+import {
+  CONSENT_CHANGE_EVENT,
+  getConsent,
+  hasConsentChoice,
+  type ConsentRecord,
+} from '@/lib/consent/cookie-consent'
+
+export function useCookieConsent() {
+  const [consent, setConsentState] = useState<ConsentRecord | null>(null)
+  const [ready, setReady] = useState(false)
+
+  const refresh = useCallback(() => {
+    setConsentState(getConsent())
+    setReady(true)
+  }, [])
+
+  useEffect(() => {
+    refresh()
+    const onChange = () => refresh()
+    const onStorage = (e: StorageEvent) => {
+      if (e.key === 'memento-consent-v1') refresh()
+    }
+    window.addEventListener(CONSENT_CHANGE_EVENT, onChange)
+    window.addEventListener('storage', onStorage)
+    return () => {
+      window.removeEventListener(CONSENT_CHANGE_EVENT, onChange)
+      window.removeEventListener('storage', onStorage)
+    }
+  }, [refresh])
+
+  return {
+    consent,
+    ready,
+    hasChoice: ready && hasConsentChoice(),
+    needsBanner: ready && !hasConsentChoice(),
+  }
+}