ui(consent): persist cookie-banner choice in a cookie (365-day) + localStorage

Previously the banner only wrote bb_cookie_consent to localStorage. Many
browsers wipe localStorage in strict-tracking-prevention modes, on
"clear site data on close", and in some private-browsing-adjacent
profiles — so the banner re-appeared on every visit even after the
user clicked Accept or Decline.

Now writes to BOTH a `bb_cookie_consent` cookie (path=/, max-age=365d,
SameSite=Lax) and localStorage. Reads from cookie first, falls back to
localStorage for backward compatibility with prior visitors. Banner
stays hidden for 365 days after a decision is made.

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

src/components/CookieConsent.tsx

@@ -2,21 +2,41 @@
 import React, { useState, useEffect, useRef } from "react";
 import Link from "next/link";
 
+const CONSENT_KEY = "bb_cookie_consent";
+const CONSENT_DAYS = 365;
+
+function readConsent(): string | null {
+  // Cookie first — survives most "clear localStorage on close" settings.
+  if (typeof document !== "undefined") {
+    const m = document.cookie.match(/(?:^|;\s*)bb_cookie_consent=([^;]+)/);
+    if (m) return decodeURIComponent(m[1]);
+  }
+  try {
+    return localStorage.getItem(CONSENT_KEY);
+  } catch {
+    return null;
+  }
+}
+
+function writeConsent(value: "accepted" | "declined") {
+  // Write to BOTH so we survive browsers that wipe one but not the other.
+  try {
+    const maxAge = CONSENT_DAYS * 24 * 60 * 60;
+    document.cookie = `${CONSENT_KEY}=${encodeURIComponent(value)}; path=/; max-age=${maxAge}; SameSite=Lax`;
+  } catch {}
+  try {
+    localStorage.setItem(CONSENT_KEY, value);
+  } catch {}
+}
+
 export default function CookieConsent() {
   const [visible, setVisible] = useState(false);
   const acceptRef = useRef<HTMLButtonElement>(null);
 
   useEffect(() => {
-    try {
-      const consent = localStorage.getItem("bb_cookie_consent");
-      if (!consent) {
-        // Delay slightly so it doesn't flash on first paint
-        const timer = setTimeout(() => setVisible(true), 1200);
-        return () => clearTimeout(timer);
-      }
-    } catch {
-      // localStorage unavailable (SSR or private mode)
-    }
+    if (readConsent()) return; // already decided — stay hidden
+    const timer = setTimeout(() => setVisible(true), 1200);
+    return () => clearTimeout(timer);
   }, []);
 
   // Focus the accept button when banner appears (accessibility)
@@ -27,16 +47,12 @@ export default function CookieConsent() {
   }, [visible]);
 
   const handleAccept = () => {
-    try {
-      localStorage.setItem("bb_cookie_consent", "accepted");
-    } catch {}
+    writeConsent("accepted");
     setVisible(false);
   };
 
   const handleDecline = () => {
-    try {
-      localStorage.setItem("bb_cookie_consent", "declined");
-    } catch {}
+    writeConsent("declined");
     setVisible(false);
   };