Fix GA measurement ID and CSP, redirect legacy Hugo URLs

Use the GA4 measurement ID Search Console expects and allow Google Tag Manager/Analytics in the CSP so gtag is not blocked. Add 301s from the old /posts, /writings, /tags, /archive, /about and /index.xml URLs to their current routes to clear the Search Console 404s.

src/app/layout.tsx

@@ -59,7 +59,7 @@ const websiteLd = {
 };
 
 const isProd = process.env.NODE_ENV === "production";
-const gaId = "G-9XLTKZF07C";
+const gaId = "G-4HGRQ9QNPD";
 
 const umamiScript = process.env.PUBLIC_UMAMI_SCRIPT_URL;
 const umamiId = process.env.PUBLIC_UMAMI_WEBSITE_ID;